I've read that the "Bis" option is currently used to organize issues with the same number (so the option with Bis checked will be organized as a ".5" and come after the one not marked Bis) but this doesn't seem to change anything in my collection. No matter which file is marked as Bis or whether the title's are in alphabetical order, the order never changes and it is in the order I don't want. Am I just using Bis wrongly?

That’s the right way of using it. Do you have numbers assigned to your comics? Is this in iOS?

I had the same issue numbers assigned to both files. This is on PC