I've been using Ryzen 7 2700X for about 6 months and everything works fine. I recently noticed some wrong temp readings in FreeNAS UI and sysctl but that's about it. I also have overclocked RAM with absolutely no issues. I had problems with sticks working nicely together (had to up the voltage a bit). Ran memory tests for about a week and that too passed.
@Apollo Have you had wrong temp readings with your 1900x ?
I'm new to FreeNAS and set it up on a few year old dell latitude laptop I had laying around. It worked great, so I decided to build a PC without doing my research on AMD processors. I went with AMD because of the significant cost difference over its Intel counterpart. I am currently running FreeNAS 11.2-U4 with no issue other than the OS reading a high CPU temperature as well. It threw me off when the Dashboard was showing me the CPU was running in idle at 80C. I immediately shut it down and hooked a monitor into it and booted into the BIOS where it was stabilized idling at 35-41C. I contacted support and created a ticket (NAS-101802) and received cursory feed back stating the below.
"I suspect this problem is already be fixed in FreeNAS 11.3 nightly builds. You may backup your configuration and try to update to check it. There was 49C shift introduced at some point, so your 82C should be really 33C."
I noticed the nightly builds are labeled as "Very Unstable". From how I read your post, the temp reading wrong is nothing to be concerned about.
I've held off purchasing HDD storage to complete my build until I get this resolved either in the OS or my mind.