Why do Streaming sites from the megathread keep stopping randomly?

Hi! I have a bit of a problem from the various streaming sites from the megathread. Recently, I started streaming series and movies instead of downloading because I don't have enough storage space and almost all the streaming sites from the megathread either stops randomly or just doesn't play at all. I don't think my internet speed is the problem since I have a gigabit connection but I wanted to find out what causes it and get it fixed. Any help would be greatly appreciated!