I use UbuntuStudio 18.04.2 LTS (64 bit Linux) and MuseScore 3.0.5 (last official available version, not the Portable AppImage).
I have a very weird rare with this software: each time I start this app... I don't get sound from it!
I have to perform a very rare internal procedure (inside MuseScore) to get sound:
Inside the "Preferences" Menu, Input/Output tab, MuseScore has a button labeled as "Restart all audio and MIDI devices". I have to click on that button to get sound. It is this way almost each time I start MuseScore.
BTW: I use ALSA audio system with MuseScore because the other options (Pulse and PortAudio) gives me some random clicks and pops while the music is sounding. The other possible audio option is JACK but I don't know how to use it.
With the older versions of this software I didn't have this issue.
Can somebody tell me something about this issue?
Maybe some audio library incompatibility? ???
Sadly, anything installed from outside of the official Ubuntu repositories is not supported here. However, we (the Ubuntu Studio team) are aware that the version of MuseScore in the repositories (which is inherited from upstream Debian) is outdated as of this writing, and are currently working on getting that updated in Eoan (future 19.10) and likely added to our backports PPA for 18.04.
Futhermore, PortAudio is not available in Linux as that's an older Windows audio API.