[notum]

https://www.youtube.com/watch?v=QvTmdIhYnes

Modern camera firmware detects stuck and dead pixels and tries to fill them in with neighbor data., but when there's too many... there's not enough data to fill in.

Keep watching top left part of the video. Most visible at 0:30.

[petertodd]

Actually at the very end when they go into a dark place is the most visible. The whole sensor is covered with defects.

[rambojazz]

Maybe it's me, maybe it's the screen, I can barely spot any dead pixel at the 00:30 mark. But at the end of the video it's very clear. Thanks for pointing it out.