Canon 300 2.8 IS focus hunting

This fall I've had some issues with my Canon 300 2.8 IS/1D Mk IV combo not wanting to focus. During football season I had times where the focus would just hunt and not want to lock on when using AI servo. I've never had this happen in the past. The problems would last a few minutes, and then the problem would seem to go away once I pointed toward a very well light high-contrast subject. I wrote it off as bad lighting, even though I've never had problems on the field in question.

I ran across the same situation last Friday when shooting basketball. The light in the gym wasn't too bad (1/800, f2/8 ISO 6400). My 70-200 2.8 IS II lens had no problems locking on at all in AI servo on that night. Again, last year I had no problems with the 300 in similar situations.

My question is has anyone else had similar symptoms or had their 300 2.8 IS repaired for focus problems (and what was the diagnosis)?

I have never had a problem with that combo. The only time my autofocus hunts is when I have stacked both of my extenders (f/8) which is rare.

The bare lens focuses very fast even in poor lighting.

Tapeman wrote in post #15264837
I have never had a problem with that combo. The only time my autofocus hunts is when I have stacked both of my extenders (f/8) which is rare.

The bare lens focuses very fast even in poor lighting.

Thanks a lot....I've never had a problem either until this fall.