Possible bug in RVIZ

I was working on the RVIZ in the RTAB course. Whenever there is a situation where a new window opens, the window open as usual, but after a couple of seconds it resizes to a smaller version, leaving a black space as shown in the screenshot. Everything still works as it should but the resizing situation is a
bit frustrating.

Please look into it. Let me know if you need more info.