I could also try to check why JACK is not getting permission to use Realtime Scheduling.

Turns out this can be fixed by adding itself to "jackuser" group.

So, even if, for whatever reason, is not desirable to have JACK working together with PulseAudio...

Would be interesting, nonetheless, add all users to "jackuser" group by default, to prevent users have a not so good experience with JACK Apps?

(sorry for bad English)