What's going on here

[Birman]

As you can see from the video, the liquid in the pipes just stops flowing for no obvious reason. It always follows the same rhythm - 3x10kg liquid blobs get through and then it pauses. I tried reloading - no change. Tried deconstructing and rebuilding - no change. When I diverted the flow into the pipes above the problematic area then everything worked perfectly fine. When both pipe paths are connected, the bottom one just stops completely and only the top one works. I have no mods that change the piping. I'm not sure when it started exactly, but I think most likely since the last update. So far this seems to be the only loop that's behaving like this.

[Zarquan]

I don't know if its just me, but I can't see your video.

[DolphinWing]

Not sure what's on the right side of the entire system. We can't find what exactly happen to your system.

Maybe you should take more screenshots of the system or attach the save file.

[melquiades]

Absolutely no clue. But a full picture of the system would be nice to see.

Try adding a liquid bridge to see if it skips that area.

@Zarquan Yeah it doesn't play, i had to save it to my pc to see the video.

[Gurgel]

You probably have added some buildings or liquid bridges or switched something on or off outside of the screenshot that make the flow-direction algorithm fail. As this algorithm is high effort and needs to run whenever anything in the pipe-system is changed, it is just a partial implementation and cannot deal with all situations. The common fix is to add bridges to force a direction. 

[Birman]

After posting this I left it with the bypass, because that flow delay was causing the system to overheat slowly and I couldn't let that happen.

I hadn't touched that loop for many hundreds of cycles, it has just been running on its own this entire time, so no structural changes had occurred. It's most likely just what Gurgel mentioned that the algorithm failed there for some unknown reason. After a couple of saves and reloads the issue has fixed itself (the flow runs smoothly with its original pipe path). 

[Gurgel]

Might be some race-condition, i.e. critical timing dependency. Partial algorithms often have that issue. I usually am simply very generous with bridges. That also reduced the computing effort overall.