@paulakreuzer: Maybe thats interesting for solving this problem in the future:
I have the same problem with my sensor. Cleaning solves the problem every time.
I saw that the seal of the sensor isn’t saved from dust. The seals of the other sensors (on the inside of the display) are higher than the display. Only the Proximitysensor-seal is lower than the display. So dust can come in.
Sorry for my bad english… for better understanding i made some pictures:
Here you can see it best:
For me its a manufactured failure… Changing the Display with one with a correct seal would solve…
Regards,
Jonas