It's pretty tricky making split patches. I have some banks saved that can bring up a split patch. If you save one of the layers of the split in the same bank as the other layer that is the A portion, then you can reload that bank and mark it in your files as a bank that has a split or splits in it, and get the same sound because both layers are in the bank.
So you go UNI + ^ and it takes you to split, and then you select the layer you want to be operating on. Then when you save it, A goes to the button you save it to, but the B portion is someplace else. Typically you surf to the B program you want while it is set to change B, then you select that and it becomes the program for B.
If you work on your b portion, actually it may be that you must save it to a separate button. Best to test that part first, and make sure what you save is what you were working towards in the B layer. When you go back to the split button and bring it back you will hear the same A layer but the B will still be pointed to the original program that B was. So you may need to change it to the newly saved button see? So best to save it into the same Bank if possible. It's pretty fundamentally difficult to conceptualize how to save your changes. So save the B first (if you changed it) to another program in the same bank, that's how it works best.
I may have misspoken about this so don't quote me. But the B portion MUST BE SAVED separately. I am not at all sure if it won't be saved as a split. It's tricky.