I’ve had this problem a few times, and I can’t find a way to reliably repeat it.
I have a container control embedded within a window. When it is resized, sometimes I can get the resize to show, other times not.
A good example is resizing it to only show the top 20 pixels (like it’s been collapsed). The entire container control shows. I have to bring other windows in front toggle the size a bunch of times and then finally it will show up right.
Initially I only saw this on Windows. Now I’m seeing it on Mac too.