Creating a vertical split with the sidebar open causes the leftmost two columns of the leftmost vim window to get stuck and stop updating. With line numbers on, this means that I get two columns of "stuck" line numbers, and then the normal line number columns. This also affects the first two characters of the command line at the bottom. It also occurs whether the sidebar is on the right or the left. Here's a pair of screenshots:
iirc this is related to the experimental renderer. Can you check in the preferences if you have that turned on and try it without it?
Confirmed -- disabling the experimental renderer fixes the problem. Thanks for your help!