I'm not quite sure. It's possible it was IS related although the lens never made any odd noises.
Canon is typically fairly cryptic on their repair notes. I was actually pretty impressed that they cited an electrical problem in the lens versus their usual "fixed...works" comments.

I tested the camera today with the 70-200 mk1 and the issue doesn't seem to be there, so looks like a lens issue rather than camera...
They're both going back to canon tomorrow and will be apparently looked at as a priority as the issue wasn't fixed last time...
The engineer said they have no facilities for testing AI Servo - only one-shot. I might ask him to go out into the car park with a colleague to test it... Real world testing!







