fabi.png

So, I did a little more testing and randomly found out that the issue entirely disappears when I place transparent blocks like glass:

During my tests in (mainly) 1.21.11, I noticed that everything works fine as long as there are no entities visible on the screen. However, when there is at least one entity currently being rendered, the bug description matches my observations. (it works depending on the block-outline being visible, which seems odd)

Maybe this helps narrowing down possible causes.