Placed a double chest full of 5 item types that were filtered in the Sorter, and one that wasn't.
When the sorter got to the item that wasn't in the filter, it stopped. When I removed the item, still didn't work. When I resorted the chest's inventory, started running again...

EDIT: the items seem to be getting stuck in the lower half of a double chest... Looks like the machine is only seeing one chest...

Double chests are the original multi-block. They have always been massive pains in the butt requiring special inventory coding.

^, will look at it though. I thought we covered it, but missed some cases apparently