Side Bar keeps reappearing

The side bar on the right hand side of my screen keeps re-appearing, even though I have set it to be hidden several times now. It seems to be connected to switching to calendar view and back - but it does not always happen when I’m doing this.
I’d be happy to disable or remove it completely instead of having it come back again and again, I don’t need it and it just takes up screen space I’d rather have for my emails…

This issue has been addressed and the fix will be in the next release.