SD card has the same limits. Ive tried different cards, batteries, the cards have been very cool, none of these seem to change things much.This Canon chart says that it can record 8K IPB 10 bit video to SD v90 or above card. Wouldn't this mean that you could record 10 bit 8K without any CFexpress card in the slot? I wonder if you record continuously for hours this way?
Either something inside is very hot that cant be cooled easily, they are very cautious in their cooling times, or its a bug.