It's been rather humid where I live. I had the same issue earlier today.
I have a Phantom V4 LE Saberstaff.
One of my coupler ends got stuck in one of my handles.
I tried a number of things, and it remained stuck. Nothing worked.
Then I grabbed some pot holders, the canvas kind with the rubber pads on the inside.
One grip on the coupler threads, the grip on the handle the coupler was stuck in.
Twist both in counter directions to loosen. Worked well.