@markus101 Mono was definitely the problem. Thank you for your suggestion.
Here is my information:
Sonarr Version - 2.0.0.5163 (That’s when problems started, previously was on Version 2.0.0.5153)
Mono Version - 4.2.3 (previously 3.1.0)
on Docker (Unraid OS)
did docker -it Sonarr bash to get access to the container. then followed the instructions on Mono Download page for Ubuntu 16.04. Mono was upgraded from 3.1.0 to 4.2.3, problem solved.
Note: I’m a noob, if there is an easier way how to update Mono, please don’t laugh at me 