i've had it several times (fortunately enough not when performing, but during soundchecks and co):
when i change live's tempo using a controler (BCR or remote SL), the CPU jumps to 800%, live freezes.
i still can save my set.
if i click on the CPU button to switch off my soundcard and then switch it on again, the CPU is still at 800%
i'll try to remove some plugins (dBlueglitch may be the culprit) and report again.