Nicola, are you saying that, at some point, the camera app stops working? Or is the camera-app working fine and you then don't see the thumbnail for a photo you have taken?
Are you able to get a terminal session on the phone? If so, it would help us if you could send the logs for the thumbnailer and the camera-app around the time you see a new photo failing to produce a thumbnail.
Added camera-app.
Nicola, are you saying that, at some point, the camera app stops working? Or is the camera-app working fine and you then don't see the thumbnail for a photo you have taken?
Are you able to get a terminal session on the phone? If so, it would help us if you could send the logs for the thumbnailer and the camera-app around the time you see a new photo failing to produce a thumbnail.