My DG-300 sometimes gave me problems early on. What I learned is that the spoiler automatic hook-up can be not properly engaged in the first (right) wing. If that's the case, the spoiler's automatic hookup fitting on the fuselage is not properly aligned to receive the left wing. It will block the wing from coming all the way in.

My procedure is: after getting the right wing seated, I move the spoiler handle while pushing in on the fuselage's left hand spoiler fitting. This allows me to feel when it engages the right hand wing. I can actually open and close the right wing's spoiler when it's engaged all the way.

Larry
FP