It probably has nothing to do with the Fx. I found that too on my Jolla1. The last time I was using it reliably was summer 2019. Tried again in April 2020 - it worked for a few minutes, then shut off. Connected devices are still connected but have no internet. One of the recent updates must have broken it.

Update:
Sorry, I take that back! Hotspot worked again after a reboot. Probably more to do with my data connection and the fact it had not been used for a while than with the phone itself.