The splitter issue has been mentioned before.
The cause is one item being "stuck" halfway between the input and one of the outputs. Effectively blocking the splitter.
As long as the belt that has the half-stuck item on will continue to take items off the belt, it'll resolve itself automatically.
But in the case of the video, it happened when one belt was full and wasn't continuing anymore. effectively blocking the other 2 outputs indefinetely.
The solution to fix it, is to manually take 1 item off the full belt.