Occasionally, the Sonarr process will get out of control in Activity Monitor (increases to 120% or higher). If I try quitting from the web admin, the Sonarr process doesn’t quit, and then the mono-sgen64 process also goes really high, to about the same percentage. When this happens, the only thing I have been able to find to fix it is to reboot the entire computer.
Mac Mini running Sierra 10.12.6. Latest version of Sonarr and mono.