I read that this might be bad, but it appears both neutral and grounds are mixed on two different bus bars. It isn't just one wire that doesn't follow the pattern; there are several neutral wires on the predominantly ground bus bar. Should I rewire everything to separate ground from neutral? The subpanel is in my garage -- it's largely for pool equipment. It's 60A and runs from the main house underground from the primary 200A service panel. This wouldn't be the first crazy thing I discovered from the previous homeowner (eg, shelves sitting on top of upside down square brackets).
Also, would this be a reason for a GFCI breaker to be tripping instantly in the subpanel?