Yes I agree this is a duplicate of 74273.

Thank you for that detailed explanation. This "gap reduction" feature is part of the 0.17 belt optimizations I presume? Something to do with not tracking items but the gaps between them? I never appreciated how complex splitters have to be internally, from a user perspective they appear to...

Using a red splitter fixes the problem, thank you! But I noticed another thing: You can trigger the splitter misbehavior by using the F key to grab items from the lane in front of the splitter. If you do that, the splitter stops working until you release F. Doing that with a red splitter does not tr...

Yes exactly. Both left lanes of both input belts are full, so I would expect a splitter to take items uniformly from both left lanes.

However, this does not happen here. It looks like input priority is randomly switching on and off.

Check out this video I made on my PC. (I also made a Reddit thread here ) There is no input or output priority set, and the splitter is taking items from the inputs in an unpredictable way. Load the attached save file Train_2 to see the behavior. This is the autosave that happens during the video.

I just registered to tell that I really really REALLY like these changes.

Oil has always been a huge pain to set up initially, having to store two fluids with little use. This fixes it.
Now it is possible to set up blue science without rushing Advanced Oil Processing.

Thank you, devs!