[Tony Collins]

I have same problem with 2 cameras now, and as far as I can tell I think it’s a sign of the head dying (not exactly good news).
The player needs to synchronise frames, and I think that if the sync is lost it just shows a blue screen instead of a shakey picture. Maybe the sync signal is just below the threshold that the system is calibrated for (because if the head is getting tired the signal is weaker).
I think that the fast forwarding works because either it uses a different part of the head to read during fast forward motion, or the increased speed of the tape movement increases the magnetic flux just enough to pass the threshold.
Cleaning the head might help ?
This is only an educated guess, so if you ever do find out the real reason, I’d love to know too !!