What causes a milestone reward firing twice on the same threshold?

The milestone check granted the reward whenever progress was at or past the threshold, and the check ran on multiple events, so it paid out repeatedly.

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 a Milestone Reward Firing Twice on the Same Threshold

Quick answer: Track which milestones have been claimed and grant a milestone's reward only on the first crossing, guarding with a claimed set that persists.

A milestone that pays out every time the progress bar is re-evaluated will hand the player the reward over and over. Marking each milestone claimed on first crossing fixes the double-pay. Here is how.

How to fix it

1. Keep a claimed set

Maintain a persistent set of milestone ids already rewarded. Grant a milestone only if its id is absent, then add it.

2. Separate progress from claiming

Re-evaluating progress should detect newly crossed milestones, but the actual grant must be gated on the claimed set, not just the threshold comparison.

3. Handle multiple crossings at once

If a single update jumps past several milestones, iterate them in order and claim each that is newly reached, so none is skipped or repeated.

4. Persist before granting visuals

Add the id to the claimed set and save before showing the reward popup, so a crash mid-celebration does not let the milestone re-fire next launch.

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 HTML5 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.