There was a bug in the for Quip app around December 2018 that causes a number of operations to not persist in the diagram. We store the diagram as an initial state followed by a series of edits to get the final diagram. The bug caused a corrupt edit, so it's not possible to play the sequence fully. If you continue to edit the diagram, the playback will still be broken and you will lose any further changes.

On the affected diagram, click on it to show the menu. Pull down the diagram menu:

Select Preferences:

Click Compress:

And any valid edits will be integrated into the initial state. Further edits to the diagram will then persist correctly (make one change and refresh to check).

Any edits made after the invalid edit will be lost, apologies for this error.