If I understand correctly when you are using canvas for long time and using several drawings and then you execute Undo and then crash appears with "redo stack is empty".
Can you provide print screen when this error appears. It would be interesting to see History pane, to see if there is special combination of actions when Undo appears.
EDIT: Can you please also provide operating system name and version.
Affects version 2.1.1. Happened to me just now after I had been doing things on the background layer and tried to ctrl+z while some pixels were selected. Then once it started, it would not stop until I closed the project -- every click or keystroke would result in an error message box. The history pane still contained all the actions, and ctrl+z and ctrl+shift+z still worked, but the error message kept popping up. However, now that I am trying, I cannot replicate it. I will copy and paste the full error the next time I run into it and include a screenshot.
More information about how to reproduce this error is needed