I have a canon EOS C70, it's intermittently having these issues. Another acquaintance is having the same problem, and I found your issue online too. Looks like you are not alone!
Basically what happens is you'll notice the screen begins to flicker/flash, (when not recording) and it almost looks like the shutter speed is wrong and picking up artificial lighting poorly, (but that isn't the issue) and if you go to try and alter a setting or record, the camera won't respond, so you are forced to turn it off. When you try to turn the camera back on, it wont restart, almost like it's a computer crashing. We have found the only temporary fix is to remove the battery and replace it. So far, for both of us this has allowed us to continue filming as we were, hope this helps you too.
We havent noticed that it's audible to the user, but we haven't been in quiet environments and naturally when the issue occurs during filming we are panicking and trying to get it to stop quickly so we can continue filming so are not concentrating on this I guess. Interestingly, we both have the 50mm sigma f1.4 Art lens and have been using these, I am not sure if it's always happened with this lens attached but I will try to make notes of the exact circumstances in which it happens to look for patterns.
It's happened to both cameras (mine and the other persons) several times, it happened twice in one day to me on Saturday. It's interesting though because the cameras are very similar in age but their camera has the new firmware and mine isn't updated and their camera has seen much more use than mine. But the issue began happening within the same few weeks for both of us.
Have you had this issue for long, how often is it recurring etc?
PS. I contacted Canon CPS today on +44 (0) 800 9150009 and spoke to a guy called Gavin who said he would be investigating it. Have you contacted them, if not, then it would be a good idea so you can get his feedback too.
