Created attachment 114494 [details]
visual representation of error occuring

I am using krita version 4.0.3 , but i was unable to specify that in the report field and since i rather finish my current work in a "stable" environment i have no way to test it for now in a newer versions. I am pretty sure it's something i have experienced in the previous versions, at least in 4.* branch.

I am working on a big canvas (4096x7016 px) and sometimes when i try to undo the stroke, what ends up happening is that i end up with missing rectangular "chunk" of a layer i'm working on, where the stroke was present (see attachment, where i have tried to visualize that. The cyan rectangle is not something that actually shows up on the canvas, it's just here to illustrate what i think ends up getting missing, since it's always a rectangular chunk around stroke). 

It might be happening when i use undo, while the document is autosaving, but it don't really have the reliable way to test that manually. 

My other guess is that it happens when i am running out of RAM and system starts using the swap for storage.

There are no errors that end up in stdout/stderr in console.