I just upgraded from my old Mamiya 645 AFD II to the Phase One DF+ ..

On my first shoot with it and using the Leaf Aptus 22, I am finding after maybe 20 exposures, the system will just lock up.
To clear it I have to decouple the back from the body and reattach.
I checked firmware and its at 227
Anyone had this issue before ?
Cheers