HL7810 Not Responding

I am having problems getting the HL7810 to work after buying a large batch from Digikey.
Previous batches worked with no issues.
I am wondering how to debug these modems. The contract manufacturer did X-ray the modems and all connections were in good condition.
The serial AT command interface gives no activity upon a reset on the RX/TX lines although the VGPIO shows that the modem is ready.
Any possibility to reflash the firmware without access to the AT interface?

Please advise ASAP. Thank you.

Do you have the UART0 port?
You can compare if there is output in UART0 port in Ok board and NOK board.

Yes thank you. I have activity on UART0. It looks like the updated board revision has some hardware flaw with the AT UART interface.
Thank you for help.