This issue of fingerprints lost can sure cause similar symptoms. Could you maybe next time when the sensor is not working, take a look at the settings and see if there are any fingerprints shown? Personally, I haven’t stumbled upon the issue on Sailfish 4.4, but I’m thinking it’s just matter of time 
As pointed in the linked post, the following commands should fix the fingerprint daemon, and the fingerprints should be visible on the settings again.