Quick answer: Auto Size + Baseline alignment causes visible vertical jumps when text changes. Disable Auto Size and use a fixed point size, or switch Vertical Alignment to Geometry Center so the rendered glyphs stay visually centered regardless of font metrics.

Here is how to fix Unity TextMeshPro labels whose vertical position appears to jump every time the text changes. A score counter, name plate, or chat bubble bobs up and down by a few pixels with each update. The cause is the interaction between Auto Size (which recomputes point size) and Baseline alignment (which positions based on font metrics that scale with point size).

The Symptom

A TMP label with Auto Size enabled and short fluctuating text (numbers, single words) jiggles vertically as text changes. Long text fills the box and sits low; short text in big size sits visibly higher.

What Causes This

Auto Size + Baseline. When text shrinks, Auto Size raises the point size, which raises the cap height and the ascender extent. With Baseline alignment, the visual top moves up.

Padding extents change. Padding around glyphs is proportional to font size. As size changes, padding shifts the bounds.

Mesh refresh on Set Text. Each text change rebuilds the mesh; small float jitter in the layout can produce visible position changes.

The Fix

Step 1: For stable labels, disable Auto Size. Pick a fixed point size that fits the longest expected text and use it always.

tmp.enableAutoSizing = false;
tmp.fontSize = 36;

Step 2: Use Geometry Center vertical alignment.

tmp.alignment = TextAlignmentOptions.Center;   // horizontal
tmp.verticalAlignment = VerticalAlignmentOptions.Geometry;

Geometry alignment uses the actual rendered glyphs’ bounds rather than the typographic baseline. Visually centered text stays centered regardless of point-size shifts.

Step 3: For Auto Size cases, narrow the range.

tmp.enableAutoSizing = true;
tmp.fontSizeMin = 28;
tmp.fontSizeMax = 36;
tmp.autoSizeTextContainer = false;

An 8-point range produces visible but minor vertical shifts. Wider ranges produce dramatic ones.

Step 4: Pin layout to a parent RectTransform. Place the TMP inside a fixed-size parent. Anchor the TMP to fill the parent. The parent does not move; the text stays inside.

Step 5: Disable Margin contribution. Margins cause additional padding. Set all four margin fields to 0 unless you need them; they add silent vertical offsets.

For Score Counters Specifically

Score counters are particularly noticeable. The fix combines:

Understanding the issue

This bug class falls into a pattern that's worth understanding beyond the specific case. In Unity 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

This bug class disproportionately affects late-stage development. The work to surface it is interactive testing in realistic conditions, which only really happens after the gameplay is in place and assets are populated. Catching it early requires deliberate testing of conditions that look unimportant.

At the engine level, the behavior comes from a deliberate design decision in Unity. 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

For shipping games, the safest verification is a staged rollout. Apply the fix to 1% of players for 24 hours; watch the affected metric; expand if green. Skipping the staged rollout means the verification is the entire player base, which is too high a stakes for most fixes.

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

Performance implications matter when this bug class scales with player count or asset count. A bug that fires once per session is annoying; a bug that fires once per frame compounds. After fixing, profile the affected code path under realistic load. The fix that's correct for one entity may be too slow for ten thousand.

Diagnostic approach

Before applying any fix, gather enough context to be confident you're addressing the actual cause and not a similar-looking symptom. The cheapest diagnostic step is reproducing the bug deterministically - if you can't get the same failure twice in a row, your fix attempts will be hard to evaluate. Lock down the reproduction first.

For Unity-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 Unity, 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

Edge cases for this class of issue often involve specific timing: the first frame after a state change, the last frame before a transition, frames where multiple subsystems update simultaneously. Reproducing these reliably is part of what makes the bug class hard to test.

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

Document the fix and its rationale in the commit message or attached engineering doc. Future engineers will encounter related issues; the rationale tells them whether your fix is reusable or specific to the case at hand. Without rationale, the fix gets reverted or copied incorrectly.

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.

“Auto Size + Baseline = vertical bob. Fixed size + Geometry Center = stable label.”

Related Issues

For TMP emoji rendering, see TMP Emoji Sprite Asset. For TMP wrap issues, see TMP Text Not Showing.

Disable Auto Size. Geometry Center. Tabular figures. Counters stop bobbing.