With setup as in the picture when inner belt becomes full then items on that inner belt stop moving until at least one item from inner belt is picked up and there is a gap. I expected it will keep going all the time. Outer belt works all the time.
Thanks for the report however that's working as intended. The "front" of the belt has nowhere to move because it runs into the back of itself and so it just doesn't move.
If you want to get ahold of me I'm almost always on Discord.