Had the same behaviour in vitals (not on a Framework though) a few weeks back.
Values were shown correctly after a reboot
But sensors-detect was able to find my fans, so that bothers me a bit… maybe the fan is not exposed by the EC correctly…
Edit: Have a look here:
[Linux] Fan speed controller with custom speed curve - Framework Laptop / Linux - Framework Community
Not a fix, but maybe it get you in the right direction
Update: I have looked a little closer myself and cant find a resolution myself.
Will try to dig into the EC after work =)