Sometimes (about one in five) times on loading/respawning due to distance, some filters on a tech can become "semi-detached" so that they don't pass their contents to the next conveyor piece. In such state they don't show their input/output arrows at all, as seen in the image. Bugged filter circled with red. I'm have observed the same happening occasionally with Alternator Conveyors, which is what I was trying to repro here, but filters decided to bug out first. The "easy" fix for this is to reattach the filters. How easy this is depends on the design of your tech. This has been reported before, I think, but here is an easy repro case. Another thing to note is that they also drop their contents (if any) at such situation. Attached snapshot and a save too. The save has filters already in bug state. Easy repro is to reattach the filters in the save, grab the plane, fly about 600m to any distance and do a few such flyovers until resources start piling up in silos, which is easy to see from air too. I tested a number of different designs and this seems to be the only one reproducing the bug reliably. Ironically it is the first. This is probably related to, if not the same, bug that sometimes scrambles conveyor ordering.