There is something weird about the temperature reporting of, I think, "X" designated Ryzens. I've heard of it but as I don't have any I haven't followed it up. Try Google! I do definitely recall there being a 20 degree offset when measured in certain ways. I would think that the major monitoring tools would take it into account by now.

In the BIOS for my board the memory speed is shown on the Main page. If you haven't explicitly enabled XMP though, your RAM will be running at 2133 MHz (the fastest JEDEC profile) - again, that's my experience based on my hardware. You should be able to turn on XMP in the OC Tweaker page and then choose the speed manually. You should be able to select 2400 without any problem because that's the normal operating speed of the Ryzen's memory controller, L3 cache and Infinity Fabric. On my Raven Ridge APU it's a bit faster at 2933. Anything faster than that is technically overclocking (even if you don't plan to overclock the cores) and it's shown as such in the motherboard specs and RAM QVL. You might get it to work at 3200 just by setting that profile but you're pushing the memory controller and the rest of the "uncore" quite hard so you might need to tweak other parameters to get it to work reliably.

Edit: I notice that you did say which BIOS you're using so the last paragraph might not apply to you. In any case switch to the latest beta and that ought to fix your boot problem.