So based on these few messages I went ahead and flashed the DEV rom.
I did a dirty flash from stable since the DEV is a newer release and it should be possible to do so.
So far it all went well. Had a few force closes on first boot but that has since been resolved.
I haven't encountered any breaking bugs yet even though it's a dev version. No insight on battery usage yet.
I did had to enable notifications for every app again but after that is set along with the autostart and the correct permissions which did stick from the stable build, all notifications seem to arrive in time, also from apps that wouldn't send any notification on the stable build previously.
I was also able to set up approximate or exact location on a per app basis, which I couldn't set up on the stable rom. The question did popup when opening location based apps but did not seem to change anything. It feels like a crucial permission setting was missing and maybe this is also the cause of the notification issues.
I'd recommend to use the Dev rom for now as long as the stable build isn't fixed and has the notification issues, while the dev rom doesn't seem to have it.