Aha! Problem appears when I use bluetooth headphones. And problem might be deeper.
I use pipewire.
With only internal soundcard present(!) When I create project I have to connect output to my soundcard manually, save project, close. Then reopen it, and I must reconnect output by hand again. But! No weird audio disappearing while loop playing with or without latency compensation in settings.
With bluetooth headphones turned on: Start Muse, open my previously created project and output automatically connects to the headphones. Then problem with loop playing appears with or without latency compensation in settings.
With bluetooth headphones turned on I change output to internal soundcard, problem with loop still present. I save project with outputs connected to internal soundcard, reopen, it still connects internal and autoconnects to headphones.
Turn off headphones without restarting Muse, loop problem presents. Saved project with output conected to internal soundcard, reopen (without restarting Muse), loop problem is present.
Then I turn off Muse, headphones turned off, start Muse again, open the project, MANUALY connect output to integrated - and there is no problem with loop playing.
So. my conclusions are: Muse ignores my internal soundcard, and likes my bluetooth headphones and even manual connection and saving doesn't change that. With headphones turned on loop problem exists with latency compensation turned on or off. With headphones turned on loop problem exists no matter what output device I use. Is this auto connection and loop playing problems related?