Enable debug mode leads to unexpected monica-zmq-server process exit

[uhucrew]

If monica-zmq-server is used with debug output like this:
{ "type": "Env", "debugMode": true, ... }
the monica-zmq-server process terminates accidentally after about 8 years of calculation.
If exactly the same input data is used with debugMode=false it works out.

No further information can be supplied, because there is no output, the process just terminates without a message.