I can't find a good detail shot of the Jamis dropouts. So I'm just guessing here. On mine (non turn washers, yellow-right,brown-left) the cassette joint bracket doesn't line up parallel to the chain stay. I check another's with vertical dropouts (blue-right,green-left) and that cassette joint bracket points up maybe about 20 degrees.
I slightly remember when washing my bike a year or so ago that bracket disconnected when I was wiping it with a cloth. I can't remember which, but one direction loosens it and the other secures it in place. I wonder if you try to align it parallel to the chain stay, that loosens the whole bracket. But I can't tell for sure because the alignment is going to be a little different for each type of drop out and I can't figure out what the Jamis has.