I would recommend first trying this update:
There is a critical cellular radio update in 2.8.1 which addresses a specific bug that causes the radio to no longer connect after a drop in connection. Your system may be encountering this rare bug.
I’ve attempted to re-pair it several times, it never completes successfully. Is the RF module at all tied to the one used for cellular that is clearly dead?
No. The cell radio has no impact on the PowerG keypad signaling. And looking at the system other PowerG devices seem unaffected.
Out of curiosity, it looks like it may have been labeled as “Garage.” Was this keypad actually located inside the garage or was it in the home just inside the garage door? Temperature/humidity may have caused issues with the board if in a non-controlled environment.