Sonarr keeps crashing

For some reason, Sonarr keeps crashing. Here is what the log says

Message:

 EPIC FAIL: Object reference not set to an instance of an object: Object reference not set to an instance of an object

Exception:

System.NullReferenceException: Object reference not set to an instance of an object
  at (wrapper unknown) System.Threading.Monitor:FastMonitorEnterV4 (object,bool&)
  at System.Threading.EventWaitHandle.Reset () [0x00000] in <filename unknown>:0 
  at (wrapper remoting-invoke-with-check) System.Threading.EventWaitHandle:Reset ()
  at System.Threading.Timer+Scheduler.SchedulerThread () [0x00000] in <filename unknown>:0 
  at System.Threading.Thread.StartInternal () [0x00000] in <filename unknown>:0 

Does anybody have any idea what this problem is?

I can’t even get Sonarr to stay open for more than a few minutes. Sometimes it stays on for a while and sometimes not.

Many thanks in advance

This one: Native mono crashes [kernel fix released]