So since I'm unsure how to contact Kiplacon directly, I figured I'd make a post here to give it the best chance I can of being noticed. I've submitted a pull request with the code necessary to provide support for Ultracube: Age of Cube (https://mods.factorio.com/mod/Ultracube), which can be found here: https://github.com/Kiplacon/RenaiTransportation/pull/46

There's no rush as I still need to come up with the recipe/tech changes on Ultracube's side to integrate it, but I figure the sooner it gets looked the better to be able to work out if any further changes are needed to better fit Renai's existing code.

work out if any further changes are needed to better fit Renai's existing code.

I guess we'll find out lmao

So someone reported that the Ultracube support code messed up how fuel was reinserted into trains after a jump, that code was only running in Ultracube was installed at all. I moved it out of that check but idk if that messes anything up for what you were trying to do.

Ok I took a look at it, and that was entirely a mistake I made on my end. Your fix is exactly what the code should've been to begin with. I think I forgot to test things regular fuels after I implemented my Ultracube code and that's why I missed it.