In order to describe how to replicate this i will just have to dump a lot of info that might be overkill or unnecessary
I have a bus
So I have three belts that more together (like in a bus). they contains 2 resources. 2 belts of stone ore, one belt of stone bricks
when i need to path the bricks to the sides of the belts, i use filter splitters to change which belts are which (ore-ore-bricks -> bricks-ore-ore)
When i use the mod in order to see what path the stone bricks take (holding stone bricks), the first time it shows correctly the paths, but after i (full) cycle though each lane of the belt, the mods stops highlighting after splitters, or shows only 1 specific route.
This persists also to when i stop holding the stone bricks, causing now that also 4x4 balancers to not highlight correctly (showing always just one belt, again, stopping after some amount of splitters)
This bug persist until i restart the save.
If it matters (though i doubt it), there are other mods (space exploration and it's requirements).
It's also on a multiplayer save (hosting the save), though i'm the only one playing at the time or writing and discovering this bug
i did a small test, this doesn't happen when there are no filter splitters used (IE, when a specific resource which it's path does not contain a filter splitter, it works fine)
Although this not a huge issue (i don't really see myself using the "show only this items' path" option in the near future)