I got the hard reset procedure listed below from chatGPT - but buyer beware as sometimes it's wrong.
I believe I read where the system stores code in non-volatile memory. So the fact that it "lost" the code in storage sort of seems to me the keypad may have failed (memory/cpu failure). When you say you removed the connector to cycle power - did you remove the keypad on the outside or just disconnect the connector near the programming switch? I'm assuming you tried the 1 3 5 7 9 master code after you power cycled? Also, when you say there are 4 beeps after 1119 is the 4th a long beep? If so, I believe the manual indicates system error. If you haven't removed the keypad you might take a look to see if there's wiring damage or signs of excess heating on the backside. I have no idea if the reset procedure below is valid - but since your system seems dead anyhow it probably can't hurt.
Unconfirmed!! procedure from ChatGPT
Factory Reset Procedure for Essex KE-1701:
Power Off the Keypad
Disconnect power from the KE-1701 by removing the power source.
Enter Reset Mode
While holding down the [1] and [3] keys, restore power to the keypad.
Wait for Reset Confirmation
Continue holding the keys for about 10 seconds until you hear a confirmation beep or see an LED indication (if applicable).
Release the Keys
The keypad should now be reset to its factory default settings.
Reprogram the Keypad
Since the reset erases all user codes, you’ll need to reprogram access codes as needed.