What does AT!PRIID? return? You might have to clean that up, I’ve usually made it match whatever PRI currently have it flashed to for simplicity.
I had my 7455 hung up in a similar way and had to reset the NVRAM to the factory SKU defined config:
AT!RMARESET=1
That will take it back to how it came from the factory but then I would still set the PRI ID and do an AT!IMAGE=0 to clean FW/PRI slots and re-flash with your desired firmware. And finally setting AT!IMPREF to whatever you set your PRI ID to.
Hopefully something in the above will get you sorted. Cheers!