AFAIK - It's a known issue. Please refer to the below link for more information. I vaguely remember I think it was fixed in one of the versions.

https://gateway.sdl.com/apex/communityknowledge?articleName=Adding-a-new-region-should-not-affect-other-existing-region-contents-in-that-page

https://docs.sdl.com/792149/750845/sdl-tridion-sites-9/known-issues-in-content-manager

AFAIK - It's a known issue. Please refer to the below link for more information. I vaguely remember I think it was fixed in one of the versions.

https://gateway.sdl.com/apex/communityknowledge?articleName=000009269

https://docs.rws.com/792149/107667/sdl-tridion-sites-9/known-issues-in-content-manager