Description of the issue:

I have setup a splitting conveyor belt system (see screenshot) - but items appear to take the to path only to snap into the lower path as soon as they reach the edge of the splitting conveyor - same for the other way around.

Versions & Modlist

ImmersiveEngineering-0.12-80
forge-1.12.2-14.23.3.2666
Mod pack: https://minecraft.curseforge.com/projects/modern-skyblock-3-departed/files/2551885
Singleplayer

The 2nd screen shot was taken directly after the first one

After breaking and placing the conveyors again I can't reproduce this anymore.

It's a desync between server and client, where the client says go left, and server says go right. Because both of them alternate on each transfer, they remain out of sync until you break and replace, as you found out.