i would say that for some reasson you do not have the straps done up corectly,spend a little extra time puting your harness on, making sure you have the same length of excess strap pulled through on both sides.
this will ensure that the bar is sitting in the middle where it should be, pay extra attenion to the bottom strap making sure it is super tight this will stop the bar from riding up.
you can see and feel if you have not pulled the staps tight enough.
If you have a waist under 32" I would say that you should have small size instead, even still with the straps done up tight those Fusion are rock solid med or not.
Dont be a wimp pull the straps tight! if ya can still breath there not tight enough!

Hope this helps.
Luke