Phone app breaking phone call when out of foreground

[AC Question]

Hi

I have Nomu S10 rooted. I am not sure if the problem showed in the factory rom, but I would not get back to non-root in any case.

The problem with Phone app is that if during the phone call anything makes the app go out of the foreground, the phone call gets interrupted.

This makes impossible for me to open google keep, or a browser to check something, and even the alarm clock does interrupt the phone call, which is a hindrance.

I wonder, is there any way for this to be sorted? And if I wanted to flash a downloaded factory rom to just get the phone app (and other apps?) with Titanium Backup, do I need to unroot the phone?

And may this sort the problem?

Thanks.