https://forums.factorio.com/viewtopic.php?f=49&t=104156&p=577441#p577441
As I understand it, this is caused by an inherent downside given to the thrower inserters to balance them, but I think it's still a shame that this idea doesn't work.

Throwing onto a belt is more finicky than throwing into inventories. I never quite figured out why, but I think it has to do with the fact that if there's no room on the belt the items will spill onto the floor and for whatever reason it sometimes incorrectly thinks the belt is full when it's really not. In this case though the crash is because once the room fills up there's no more room to place another item. On the regular infinite map it's not a problem. If I ever figure out the belt thing though I'll let you know