What causes Unity CI reimporting the entire Library folder every run?

The Library folder is not cached, so each CI run reimports every asset from scratch, adding many minutes to builds and tests.

How do I catch this when it only happens for some players?

Capture it automatically from the player's device with the full stack trace, the device and OS, the build, and a breadcrumb trail of what they did. That turns a vague complaint into a specific, reproducible issue you can fix without owning the hardware it happens on.

How to Fix Unity CI Re-importing the Whole Library Folder Every Run

Quick answer: Cache the project Library folder keyed on a hash of assets and packages so subsequent runs restore the import cache instead of regenerating it.

A clean checkout has no Library, so Unity reimports everything. Caching Library keyed on your packages and asset hashes turns a 20-minute import into a few seconds.

How to fix it

1. Cache the Library directory

Add a cache step keyed on Packages/packages-lock.json and the Unity version that saves and restores Library/. A stale-but-close cache still saves most of the import time.

2. Key the cache so it stays warm

Use a restore-keys fallback so a partial mismatch still restores the nearest prior Library rather than starting empty, which keeps incremental imports fast.

3. Do not cache volatile subfolders blindly

Exclude Library/ScriptAssemblies only if you see corruption; usually caching the whole folder is correct. Mismatched Unity versions should bust the cache via the version in the key.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.

Reproduce it once with full context and the fix writes itself. The hunt is the expensive part.