50 amp outlet/surge protector voltage error

First time, I apologize for the long post. I hope I can get some insight, because I am completely lost.

I have an outlying shop that I installed a 50 amp outlet to using a 50 amp box with 6/3 copper wire. Testing it with a multimeter I get 120 on each leg and 240 combined, as well as 120 from the main breaker and 50 amp breaker. However, when I plug in my 50 amp surge protector it shows an error of "E2: Voltage over 132V". The weird thing is, when I plug my protector into a 50/30 dog bone with the 15 adapter the surge protector turns on with no issue showing 119V so I dont believe it's the protector.

Any suggestions would be appreciated because after checking and changing neutrals and grounds and checking the same things over and over, I have no idea the next step and I really dont want to spend thousands having a company wire something in. TIA.

For context I have a new GEARGO RV-04 50 amp surge protector.