Page 174 of the reference manual shows what's saved in a user (X7U) file.

Files of the “User File” type saved to USB flash memory
can be loaded and restored to the dedicated area in the
User Memory of the instrument (page 22).
User File Type data is as follows.
• Performance
• Arpeggio
•Motion Sequence
• Curve
• Live Set
•Micro Tuning
•Waveform
• Utility settings
• Quick Setup

According to the list, the USER Bank's Live Set should be saved when you save an X7U file. Therefore, any changes made to Live Set (User Bank) should be reflected. Make sure you are looking at the correct bank and page when viewing live set on your 2nd instrument you've loaded the X7U to.

I do recognize since you said there's a difference between X7B and X7U - that it's not the part about finding the Live Set content that's tripping you up -- so the advice above should not be that helpful (the bit about the Live Set user bank).

Also, I suppose, make sure you save obvious names so you're sure the load is done with the correct file. Adding dates to the filename can help with this.

Off-topic aside: It's sort of interesting that quick setup is saved in a user file in light of finding/testing that custom templates are not saved after you power cycle the instrument. So I would think that custom user templates would have to be loaded from an X7U every time you power on - which seems wonky.

I was assuming that if I just edited some performances and created new Live Sets, that I could save that data as a User File or a Library File. Unfortunately, neither one of those brings the new data to the other Montage 8 at church. The file is there, but the data is not there. I can successfully access the file, but the new data doesn't appear. The Live Sets are still empty. The only way I have been successful is to do a full Backup File. Unfortunately, that takes up 15 minutes to write and read. It seems such a waste to have to backup the entire instrument just to get a few new performances and live sets transferred.

Am I doing something wrong?

There is not enough information here to know whether or not you are doing something wrong.
But clearly, what you are doing is not working.

Working backwards, we assume that you are making more than minor changes when you say you “just edited some performances and created new Live Sets...”
A USER File would work if the data you create exists completely in the User Bank.
A USER File would not work, if the data you create exists or is referencing items in locations other than the User Bank.

You say “the file is there, but the data is not there.” We assume something is there, but the description tells us nothing more than what you expect to be there is not there. We need specifics in order to help...

Is the User Live Set blank or does it report “Not Found”? ...there is a difference.
“Not Found” means the Live Set data has loaded by it is not able to locate what it needs to sound. Blank is another situation altogether.

When you edit your Performances and create the Live Set... is the data referencing the User Bank?
Or are some of the Live Set slots pointing to Library data?

These are the unknowns. Can you give any more details about the Live Sets you created, and when you say they aren’t there, are they blank or “Not Found”. Thanks

Thank you so much for your responses. I was determined this morning to document each step so we could trouble-shoot easier, but to my surprise, the data transferred perfectly! I am guessing I made a miss step in my previous efforts. So, we can call this solved for now.

Just FYI, when I said the "file was there", I meant the file was there on the thumb drive, even when viewed on the other keyboard. When I said "the data was not there", I meant that when loading the file, it yielded no changes to my performances or live sets. It was puzzling because I did it multiple occasions, carefully to name the file with the date, etc. Oh well, like I said, probably a miss-step on my part.

Again, my humble thanks.
Phil