Hey love your mod! :)
Adding the Conducting Belt mod negates this mod entirely. Can this be fixed? I can't figure out what the problem is. I tested it with only Longer Underground Belt (Aligned), Conducting Belt and Creative mod installed.

Bug discussion on Conducting Belt author's side:
https://mods.factorio.com/mod/ConductingBelt/discussion/5f33356d18dc5d3c29e0a4d8

Uploading fix now.

When two belts existed with the same speed it seemed to have trouble figuring out how to update the recipes.
Moved where the speed is set and tweaked recipe modification logic.

Thank you :)