That is definitely not normal, I guess the bunch of apps you have installed overload the Pi. So I suggest either a big heatsink or a fan will solve your problem
The heat at boot lasts for a minute or two at most and has never caused a freeze. Once Sonarr and Radarr get going, it cools back down to 55-60C and doesn’t overheat again until the idle freeze thing happens.
CPU usage by kodi hangs at about 10-15% and mono occasionally uses 5%. Nothing extraordinary.
It’s the heat after the long idles that worries me and causes the crashes.