Factorio Forums

When splitting a belt that has different items on each half and splitting again with a filter on it, items will occasionally completely stop being filtered. For example, A belt has sulfur on the left side and red chips on the right. A splitter is placed, yielding two belts with sulfur on the left and red chips on the right. Optionally, add one or more belts after one of the splitter ends. Place another splitter at the end of one of the split ends and filter it for red chips. Wait for roughly an hour, then wonder why science has completely stopped. Discover that the splitter responsible for filtering the red chips has completely stopped working. This has happened to me on multiple occasions, regardless of all the mods I play with (including vanilla), which changes after almost every game i play. If I set a splitter to filter out items, even if it comes from a split source, I expect the filter splitter to always function.

Please note that the issue also is apparent if you filter for different items, such as green chips. For issue timing, it can greatly vary. Sometimes it stops within 10 minutes. Other times it can function for an hour before suddenly stopping for no reason. Removing the filtering splitter and reconstructing it will filter again as expected, until it doesn't again. The splitters and belts were never damaged from enemies.

Attached is a picture explaining a possible setup and the log.

That looks like the splitter is working properly. Can you post a screenshot of the splitter working incorrectly, and maybe also a save?

The obvious cause I can think of is if the red belt lane got contaminated with some other items. Those items would end up on the left lane of the unfiltered output. If those items back up to the point that a non-red-cicuit item is held in the splitter's buffer for the left lane, then it will stop accepting items (including red circuits) until it can empty that item buffer onto the unfiltered belt. It won't be visible because it is held internally, but you can check if there are items blocking the unfiltered output lane and pick then up with the F key.

You are correct that the screenshot I provided shows the filter splitter working correctly. I was too panicked to take a screenshot of the issue I described, but I will the next time it happens (no idea when). Strangely enough, it hasn't happened again yet in my save.

Regarding the filter being blocked by other items, I cannot 100% for sure state that is not the issue. Would definitely explain why deconstructing and reconstructing solves it.