What causes an update manager breaking when a system unregisters during its tick?

A system called Unregister on the update manager from inside its own tick, mutating the list the manager was iterating and skipping or double-ticking other systems.

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 an Update Manager That Breaks When a System Unregisters During Its Own Tick

Quick answer: Queue register and unregister requests during the tick and apply them after the loop completes, or iterate over a snapshot so mid-tick changes do not corrupt iteration.

Replacing many Update() calls with one update manager is a common optimization, but it must handle systems that add or remove themselves while being ticked. Mutating the list mid-loop corrupts iteration.

How to fix it

1. Defer list mutations

When a system registers or unregisters during the tick, push the change into a pending queue and apply it after the iteration finishes.

2. Iterate a snapshot

Tick over a copy of the active list so additions and removals to the real list during the frame do not affect the current pass.

3. Handle removals by marking

Mark a system inactive instead of removing it immediately, then compact the list once per frame, which avoids index shifting during the walk.

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.

Most of the time the fix is small. Seeing the failure clearly is the part that actually costs you.