Crossings do not seem to play nice with process time 3 equipment.
The purplish material is input for the UV curers, and the white material is output from the chromatographs which come after them, and they should cross smoothly with the first crossing advancing the input belt twice for each time the chromatograph outputs (because one direction should flow freely if there’s nothing waiting for a turn to cross its path). With the output collector belt (taking the white material to the Ionizer) spaced with a gap between it and the input belt with the crossings, as shown, so that there’s a straight belt section between them, this is indeed how it works out unless things get jammed up somehow.
But if the belt is positioned as in the next screenshot, when that first crossing accepts an item from the chromatograph’s stubby output belt, it forces the T junction opposite that stub to roll the white material toward the ionizer, even when the crossing itself was empty at the time and nothing moves onto the T, creating a gap in what should be a process time 1 line. It seems like an “obvious solution” to have the T junction roll the item waiting along the straight portion of the output collector belt forward if the crossing itself was empty. In other words, to check if it’s possible for the waiting line of items to advance into the T, toward the ionizer (despite the crossing pulling an item in from opposite the T), so that no gap appears, the same way everything advances when there’s the straight belt in between the crossing and the T.
In the first screenshot, one of the white material coming out of the chromatographs took a left turn instead of going straight (and is now trying to go into the last UV curer for a second ride). Crossings acting like corners seems to occasionally happen when playing with the belts or resetting machines by picking them up and putting them down again, but in this case I had just reloaded the game.
Ignore the blue item chasing the gap in the second screenshot, it’s apparently the result of a mixer crossing error, only having traits of the base material. Probably also happened on game load, and just took a few cycles to reach that point right as I managed to grab a screenshot as the belt advanced and left a gap on the T.