Notes are different volumes...

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but their volume bars are all the same in Piano Roll. What gives?

I have 10 notes per loop and the 6th note is quieter than the rest. On the second loop all the notes are quieter, and the third and fourth loops are the same as the first and second respectively.

Any help? I'm super new to LMMS so... pretend you're talking to a child here. :D
Mute instruments one at a time and see if the notes could be played from overlapping notes from somewhere else.
-and, actually- in one and same notecontainer you can have overlapping notes -eg two or more notes at the same posistion. You wont be able to see anything diffrent in the note-volume window, but the overlappers will sound weird.

Play the piece at say 10-15 bmp and listen where the boosted notes are placed, then see if you have dublet-notes in a 'stack' at those posistions- just move the suspicious notes with your mouse.

Br.