Undo sometimes makes some regions in slice disappear

[katjaq]

This is a bug report

What is the current behaviour?

I drew a region, I saved, I selectively adjusted points – and I caused a slight displacement of the entire region instead. Hitting undo made this one and another region disappear (the region another logged user had drawn, remained visible). Regions did come back upon redo (or redo-- and on undo they come back?) But they definitely were all back upon page refresh.

What is the expected or desired behavior?

Undo should undo the last action only.

Version information (for bug reports)

• Browser + version: Chrome Version 86.0.4240.111 (Official Build) (x86_64)
• Your OS and version: iOS , but also on MacOS (Mojave 10.14.6)