I don't have any experience with Blue ox, but have had this happen a few times on my road master. The cause was debris on the internal portion of the latch. Doesn't help when connected.
My solution for the RM to get disconnected was to slowly push the tow vehicle towards the RV to create pressure towards the close. I was then able to release the arms.
Once released, it is time to do the full cleaning procedure for the tow bar, which from RM required full disassembly. As I don't have any experience with Blue Ox, you should probably solicit their direct advice on full cleaning.
Use caution when pushing the tow vehicle forward. I use drive, and very little skinny pedal. Usual a touch above idle just to create some pressure. Make sure you are applying equal pressure to both sides of the arm.