[youtube]https://www.youtube.com/watch?v=tTQ5uq6PyUg[/youtube]
The Canon C300 Mark II appears to have a firmware bug. This will need a fix from Canon if the C300 Mark II is to be completely bullet-proof on a shoot.
Highlights burn to black in certain situations (as with car headlights or the sun).
I hope Canon will fix this swiftly, just as Sony did on the A7S II (around 2 weeks).
Well done to Amadeusz Andrzejewski for reporting this in his amazingly detailed review of the C300 Mark II here (in Polish).