N3048 won't stack

I have a N3048 (firmware 6.2.6.6) and I acquired a second N3048 (upgraded its firmware to match 6.2.6.6). I want to use the mini sas stacking ports on the rear of the switches to stack them. In accordance with this article, I powered down the switches, connected the cables, powered up the existing switch to be the master (able to manage via console), then powered up the switch that should join to create the stack. They both boot independently and show that they are their own management switches, not in a stack.

The stacking ports show LINK and ACT lights and the console shows "Link Up" on both ports for both switches. Both switches appear to be transmitting via the stack port, but nothing is received on either end. The intended master switch is essentially full and in operation. The new switch to stack has nothing plugged into any port except the stack ports.

I have an open case with Dell Pro Support, but so far no resolution on this so I'm reaching out to the forums to find the hidden gurus.

Thank you for your expertise!