Minecraft version & Mod Version:
1.12.2 - 1.7.6

Single player or Server:
Server

Describe problem (what you were doing / what happened):
I have 2 export cables exporting the same item from the same network, one is at priority 5 and exports the single item, the other at priority 0 and also exports some other items. Both have a single stack upgrade and 3 speed upgrades. For some reason the lower priority 5 grabs the items first.

I am presuming this is happening because the higher priority cable is taking additional time by exporting other items, and as such negating the priority.
This also makes me think that this is either not fixable or would require a big rewrite of the export cable, but I figured I'd report it anyway.

Managed to get a neutered semi-functional workaround for this issue by simply removing the upgrades from the priority 5 export, making it slower.