Sorry not to respond sooner, but have been out.
For the 8124, that code is only generated when the PLC doesn't see the input from either the bayplate or backup photoeye while the machine is not armed. Most likely, these would generate due to being misaligned or dirty, but you could also lose the input if something were pulling down the voltage to the 24VAC signal. If it happens when you are busy, everything will be wet, and best chance for something to short. You could have a prox somewhere or something that would pull down the input voltage and cause that issue. I'd check wires 25 (24VAC common) and 26 (24VAC hot) to see what you read with the machine at rest, but when wet. If you are around 22V, something is shorted.
The 8820 code is rear endstop on a SGMX3 coming on at a time when it's not expected. If the face is shaved, that would drive that code, and could easily pull down the voltage.