Guitarix not working

[rva1945]

I am running 20.04 as a fresh install. Installed Guitarix. When I run it I get

20:24:52] system init *** mlockall failed:
[20:24:54] PitchTracker *** error creating realtime thread - tuner not started

Of course Jack is running.
Rakarrack i installed as well and runs fine, though with bad latency.

One more: how can I play a MP3 along with Rakarrack or Guitarix?

[Yellow Pasque]

https://sourceforge.net/p/guitarix/bugs/69/#4594