Hey,
I've noticed that in setups with pipes and underground pipes, sometimes when i move an underground pipe, some other part of the pipeline breaks.
I doesn't happen everytime, but it seems to happen more when the pipes are being used by machines, so to reproduce:
1. setup some pipeline with machines providing liquid and machines consuming it, in my case there are always some underground pipes at max range
2. move an underground pipe closer to where it starts, then add a normal pipe to close the circuit
look over the whole pipeline, if the bug triggered, you'll find something like this somewhere:
https://forums.factorio.com/download/file.php?id=88465
This sometimes leads to weird behavior of fluids shifting to a different pipeline, the picture also shows this since those pipes originally had lubricant (the underground pipe that i moved is not visible in that screenshot.
if you need help reproducing the issue let me know, i might just end up providing a savefile if this proves tricky to reproduce on your end