A while ago I noticed a weird issue with volumes, but it wasn't until I had this gig where I went stereo that it came out.

What do you mean by 'where I went stereo'?

The Montage is 'stereo' by default. It can produce a 'balanced' MONO output if you use ONLY one cable plugged into the L/Mono output jack on the back of the instrument.

The left output seems to be cranked up and the right side is very low. I don't know if I inadvertently changed some settings. I had cleaned it already and it isn't that.

Can you describe the cables (balanced/unbalanced) and how you have things connected?

1. how many cables are you using?

2. are they balanced or unbalanced? The montage has balanced outputs.

3. are you using both the L/Mono and R output jacks?

When you do a full backup (create an X7A file) you will have everything backed up including all of your library slots, user data, songs, etc.  The purpose of this kind of backup is, or one of them, is to be able to create a backup of your home keyboard and bring the file to a gig where a random Montage is being provided then you can load this file and have the same exact everything as your home keyboard.

With a good backup of this kind (and by that, I mean the filesize makes sense and that the USB stick isn't faulty) then you can safely initialize the keyboard fully since the backup file is there to put you right back where you were before.

Now if there's some setting tripping you up - then these settings should mostly be restored from the backup.  So you may still need to look at setting related kind of issues.

I'm not aware of a global setting that would take a preset that's meant to be stereo (CFX+FM EP, for example) and make the right or left channel substantially lower.