About a week with 2 prints, and yesterday it happened again. As usual after a day with and without WiFi and BT access. My feeling is that this is related to my issues with MMS as they have been one of the reasons I have been fiddling with the WiFi connection.
After sailfish-fpd restarted twice they are back as usual.
EDIT 2021-08-30: This morning they where vanished again, so sticking with only two prints don’t seem to do any difference in my case. END EDIT
EDIT Again 2021-08-30: After my previous edit I have been working from home and before lunch I lost the fingerprints twice. This time I have not had WiFi or Bluetooth enabled so right now I am totally confused, as this seem to be the trigger on the previous events. And I have not been in or out of different cellular antennas as I have been stationary at one place. END EDIT Again