FCB 1010 pedal loses its calibration

Lately the left of the FCB 1010 pedals loses its calibration and function regularly. It is programmed as wah and occasionally pedal pitch.
Let's say I calibrate it at the beginning of rehearsal and have to re- calibrate due to malfunction mid rehearsal.
This is really annoying and getting on my nerves.
I assume it's got to do with the internal sensor and I should open up the unit?
Any other ideas or suggestions?
The right pedal (programmed as volume) works properly.

Thanks Paul, I think I will certainly turn a few screws and look for the left sensor.
I'm still a bit baffled about this because the unit has always worked properly and it certainly didn't get much abuse during the summer break.
I only use the FCB when playing with the band, not when I play for myself.

Thanks for the encouragement. Will keep you posted.

Finally got to open my FCB today.
To my surprise there was nothing wrong with the alignment of LED and sensor but it was a bad soldering connection of the left pedal's LED which would only light up intermittently (which cannot be detected at all without opening the unit).
I resoldered the connection and everything is fine now.