My backup sensors decided to act weird again. The past two days or so I got the alarm beeping sound indicating a problem with the backup sensors. Now today, no alarm sound and the sensors seem to work OK now. This happens rarely but I can't seem to debug the issue if I can't repeat it.

 

Mine messes about sometimes, I think it could be a damp issue, it seems fine most of the time though so I have not bothered to look into it further.