Fix: Unreal DataTable CSV Import Header Mismatch

Here is how to fix Unreal DataTable CSV imports that produce empty or partially populated tables. You author a spreadsheet with item names, prices, and rarities; export as CSV; import to Unreal; and only the row keys appear, with all column data missing. Or the import fails outright with header mismatch errors. The CSV format is strict about how columns map to struct UPROPERTYs.

The Symptom

Importing a CSV to a DataTable shows the dialog, you confirm the row struct, and the result has rows but missing field data. The Output Log shows messages like Couldn't find property 'price' in struct FItemRow. Or the import succeeds but every row uses default values.

What Causes This

First column header wrong. Unreal expects Name in the first cell of the first row. Some templates use ---, RowName, or omit it entirely.

Case mismatch on data columns. CSV header price does not match UPROPERTY Price. Unreal’s match is case-sensitive.

Whitespace. A trailing space in a header (Price ) does not match Price.

Excel quoting. Strings with commas need quotes around them. Excel does this automatically; some text editors do not.

UTF-8 BOM byte. A byte-order mark at the start of the file invalidates the first header.

The Fix

Step 1: Define your row struct cleanly.

USTRUCT(BlueprintType)
struct FItemRow : public FTableRowBase
{
    GENERATED_BODY()

    UPROPERTY(EditAnywhere, BlueprintReadOnly)
    FString DisplayName;

    UPROPERTY(EditAnywhere, BlueprintReadOnly)
    int32 Price;

    UPROPERTY(EditAnywhere, BlueprintReadOnly)
    FName Rarity;
};

Step 2: Write CSV with matching headers.

Name,DisplayName,Price,Rarity
sword_iron,"Iron Sword",100,Common
sword_steel,"Steel Sword",300,Uncommon
sword_legendary,"Legendary Blade",5000,Legendary

First column header is Name. Subsequent headers match UPROPERTY names exactly. String values with potential commas are quoted.

Step 3: Save without BOM.

# If exporting from Excel, choose "CSV (Comma delimited)" not "CSV UTF-8"
# Or remove the BOM with sed
sed -i '1s/^\xEF\xBB\xBF//' items.csv

Step 4: Import via the editor. Drag the CSV into the Content Browser. In the dialog, choose your row struct (FItemRow). Confirm. Open the resulting DataTable; you should see all rows with all columns populated.

Step 5: Reimport when the source changes. Right-click the DataTable, choose Reimport. If you moved the source file, choose Reimport With New Source File instead.

JSON As An Alternative

If your data has nested structs or arrays, JSON imports cleaner than CSV:

[
  {
    "Name": "sword_iron",
    "DisplayName": "Iron Sword",
    "Price": 100,
    "Rarity": "Common",
    "Effects": ["Slash", "Bleed"]
  }
]

Same import dialog, picks JSON automatically by extension. Field names case-sensitive but no need to worry about CSV escaping rules.

Validation Workflow

Always import to a temp DataTable first, inspect, and only then replace your production table. Unreal’s reimport overwrites without warning, so a bad CSV can destroy hours of designer work.

Understanding the issue

This bug class falls into a pattern that's worth understanding beyond the specific case. In Unreal Engine, the underlying behavior is shaped by how the engine layers its abstractions - the public API you call, the runtime systems that respond, and the platform-specific implementations underneath. A bug at any layer can produce symptoms that look like they originate at a different layer. Triaging effectively means recognizing which layer the symptom belongs to, even when the gameplay code is what's visible.

The specific bug described above is the kind that surfaces during integration rather than unit testing. It depends on a combination of factors: the asset configuration, the runtime state, the platform's specific behavior. In isolation, each piece looks correct; in combination, the bug emerges. This is why thorough integration testing - playing the actual game in realistic conditions - catches things that automated tests miss.

Why this happens

The triage path for this kind of bug is long. The symptom appears in gameplay, but the cause is in a different system. The reporter describes the gameplay effect; the engineer has to translate that into a hypothesis about the underlying cause. Misdirection is common.

At the engine level, the behavior comes from a deliberate design decision in Unreal. The engine team chose a particular trade-off - usually performance versus convenience, or generality versus specificity - and that trade-off has consequences when you push against it. Understanding the trade-off is what turns 'this bug is mysterious' into 'this bug is the expected consequence of this design'.

Verifying the fix

Verifying this fix in isolation is straightforward: reproduce the bug, apply the change, confirm the bug no longer reproduces. The harder verification is regression - did this fix introduce a new bug elsewhere? Run your standard regression suite, plus any tests that exercise the same code path with different inputs.

Reproducibility is the prerequisite for verification. If you can't reliably reproduce the bug pre-fix, you can't reliably verify it post-fix. Spend time getting a clean reproduction before you write any fix code. The fix is fast once you understand the reproduction; the reproduction is the slow part.

Variations to watch for

There's almost always a less obvious case where the same problem applies. The reported case is the one a player hit; the related cases hide because they're rarer or affect fewer players. After fixing the reported case, search the codebase for the pattern - one fix often unlocks several.

Adjacent bugs often share a root cause. After fixing the case you've found, spend an hour searching the codebase for similar patterns. What's the same call with different arguments? The same data flow with a different entity type? The same lifecycle issue in a sibling system? Each match is a candidate for the same fix, or a related fix that prevents future bugs of the same class.

In production

Live games surface this bug class at scale. What's a rare edge case in development becomes a daily occurrence once you have a few thousand concurrent players. The class isn't 'this player has a unique setup'; it's 'one in N thousand sessions will trigger this exact combination'.

When triaging a similar issue in production, prioritize gathering data over hypothesizing causes. A player report describes a symptom; what you need is a build SHA, a session timestamp, and ideally a screen recording or session replay. With those, the bug becomes tractable. Without them, you're guessing at hypothetical reproductions that may not match what the player actually hit.

Performance considerations

If this issue manifests under high load (many actors, many particles, many network connections), profile the post-fix code path with realistic counts. The original cost was a bug; the new cost is real work, and real work has a budget.

Diagnostic approach

Diagnosing this class of bug benefits from a structured approach: confirm the symptom, isolate the variables, hypothesize the cause, and verify the hypothesis before writing fix code. Skipping the isolation step is the most common mistake; without it, fixes often address symptoms while the underlying cause continues to produce other variations.

For Unreal-specific diagnostics, the editor's profiler is the canonical starting point. Capture a representative frame with the symptom present; compare against a frame without the symptom; the diff often points directly at the cause. If the symptom is non-deterministic, capture multiple frames and look for the pattern - the cause is usually a state transition or a specific input value rather than a continuous effect.

Tooling and ecosystem

Third-party plugins often provide better diagnostics for their own behavior than the engine does. If the affected code is in a plugin, check the plugin's documentation for debug modes, verbose logging, or inspector tools - these can save hours of investigation when they exist.

Within Unreal, the relevant diagnostic surfaces include the standard frame debugger, memory profiler, and engine-specific debug overlays. Each one shows a different facet of what's happening. The frame debugger reveals draw call ordering and state transitions; the memory profiler shows allocation patterns; the debug overlay reveals per-system state. Bugs that resist one tool usually surrender to another - the trick is knowing which tool to reach for first.

Edge cases and pitfalls

Platform-specific edge cases are worth enumerating explicitly. iOS handles backgrounding differently than Android; Windows handles focus changes differently than macOS. A fix that works on the development platform may not work on every target. Test on each shipping platform deliberately.

When writing a regression test for this fix, focus on the boundary conditions that surfaced the original bug. Tests that exercise the happy path catch obvious regressions; tests that exercise the boundary catch the subtler regressions that look like new bugs but are really the original returning. The latter are the tests that earn their keep over the long life of the project.

Team communication

When this bug class affects multiple teams (often the case for cross-system issues), early communication prevents duplicate work. The team that owns the symptom may not own the cause. A 15-minute conversation at the start of triage often saves hours of independent investigation.

If this fix touches a system several engineers work in, a short writeup in the team's engineering channel helps. Not a full design doc - a paragraph explaining what was wrong, what's fixed, and what to watch for. Future engineers encountering similar symptoms will search for the fix; making it findable is a small investment that pays back later.

“Name in column A. UPROPERTY-exact headers everywhere else. Quote strings with commas. The import succeeds.”

Related Issues

For DataTable row lookup failures, see DataTable Row Not Found. For data asset cook issues, see Data Asset Soft Ref Null.

Headers match UPROPERTY case-sensitive. No BOM. Quote tricky strings. Import sticks.