Ofcourse, could also be related to heat. I've got heatsink frency on
my PPC board and added a heatsink to the 040, the programmable logic
chips between the two memory rows closest to the oscillator cans and
to the programmable logic chip at the bottom side of the PPC board.
Also, I added a fan to the 040 and replaced the PPC fan with a larger
but less crappy one. There is also a fan placed at the side of the PPC
board to create an airflow above and below the board.
Did also the same to the CyberVisionPPC board.
Simple way to test the need for a heatsink is to run your amiga with
the lid of and after some time of use try touching different
components with your finger. If you can't keep the finger on the
component you should get a heatsink and maybe a fan too.
Regards,
Göran