Hi Georg,
I will check developers what we can do with that. For Joomla 3 was extra plugin to keep session, but I am not sure if there is a J4 edition of that.
And by now, please in Global Configuration change "Session Lifetime" from 15min (default) to 30min. It should help in similar cases.
Tip #2, During edition of Page (SPPB) open a random view from Joomla Admin, and click something, go into random component, show list of modules, articles... and it will refresh session, for next period (+15min).