primal loom
What seems to happen is that the belt splitter after the catcher allows the catcher to get the next shape earlier than it should. (as in, the catcher is considered "empty" ever-so-slightly earlier due to the splitter. the same thing doesnt happen for example when there is another straight belt piece in between the catcher and the belt splitter) and because the space belt has more shapes to deliver because its more dense, the next shape actually gets onto the catcher slightly faster. The same behavior happens when a train directly delivers shapes onto a catcher. over some time, this will cause very visible desync between belts that should be going at the same speed and eventually small blockages which can add up due to train deliveries for example.
The sole reason I came across this is because I kept noticing small drops in my production that shouldn't have been there. I kept inspecting my builds trying to figure out what was happening when I eventually realized that something else is going wrong entirely.
verbal inlet
drifting basin