Quick answer: Wait for the UserStatsReceived callback before setting achievements, call StoreStats to flush the unlock, and ensure the in-game overlay is enabled so the notification can render.
When an achievement shows as unlocked in your profile but the in-game toast never popped, the unlock was committed without the conditions needed to draw the notification.
How to fix it
1. Request stats first
Call RequestCurrentStats() and wait for UserStatsReceived_t before calling SetAchievement. Unlocking before stats arrive can record without notifying.
2. Flush with StoreStats
After SetAchievement("ACH_ID"), call StoreStats(). The popup is triggered on the store, so skipping it unlocks silently on a later sync.
3. Enable the overlay
The toast is drawn by the Steam overlay. If the overlay is disabled or failed to inject, the unlock still records but no notification can appear.
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.
The errors you never hear about are the ones quietly costing you players. Visibility turns them into a worklist.