Mac loses tone signal in the middle of the session

[gfr01]

Dear All,

We are four musicians. For three of us, jamkazam runs on windows. Our drummer uses a MacBookPro16.1 with Mac OS X 10.15.4 and audio device UMC204HD. 

In the middle of the session, the audio connection to the others is broken on the Mac, our drummer no longer hears the other three. 
When he presses jamkazams "Settings" button on the Mac, the connection comes back. The other session members do not experience a loss of audio connection.
  
In the Mac-Logfile we see (please find logfile attached): 

"Audio IO callback interval is unstable. Expected 1.00. Actual median: 0.00 var: -36315952700202157443055670525952.00 - off by -100.00" 
JSB vol call back not defined 
JSB vol call back not defined 
......   x 143 repetitions
    
   
       
startMixerCleanupTimer 
Closed PortAudio stream 0x7f8ce844aba0 
PAudioOutput: Shutdown. 
  

  
Special phenomenon: 
if the bass guitar plays everything an octave higher, the connection remains constant. 
Or if only three musicians are logged in, the connection remains constant. 
  
Does anyone have a solution?


best regards,
Gerd