I just want to mention that we also experienced this during our local community event on 7 May with a regular FP6 on the latest Android OS.
Pictures taken were inititally accessible on the phone (in the camera app), but were nowhere to be found on the device just a few minutes later. Had to re-do the exercise with a different FP6 (on /e/OS and using the /e/ camera app/Open Camera) – that’s the source of (most of) the photos in the link.
Adding to the confusion, the first FP6 did not show the same error some days later during our 16 May event (I did hurry to copy all photos taken to the SDXC card in the device immediately, but they are still in both places now: internal storage and card).