What causes a puzzle undo/redo stack mishandling redo after a new move?

The redo stack is not cleared when the player makes a fresh move after undoing, so redo replays moves from an abandoned branch and corrupts the board state.

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 Puzzle Undo/Redo Stack Losing Redo Incorrectly

Quick answer: Maintain two stacks: undo pushes to the undo stack and clears the redo stack on any new move; redo pops from the redo stack back onto undo. A new action invalidates the old redo branch.

Undo/redo in a puzzle must follow a linear history with branching: once you undo and then make a different move, the old redo path is gone. If redo still replays it, you forgot to clear the redo stack on new actions.

How to fix it

1. Use two stacks

Keep an undo stack and a redo stack. Each committed move pushes its inverse onto the undo stack. Undo pops it, applies the inverse, and pushes the move onto the redo stack.

2. Clear redo on any new move

The instant the player makes a fresh move (not via redo), empty the redo stack. The new action starts a new branch and the old redo history is no longer reachable.

3. Store deltas, not full snapshots

For large boards, store each entry as the minimal change (which cells changed and to what) rather than a full board copy, so the stacks stay cheap.

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.