I realize this must be very frustrating for you but I appreciate the detailed testing and feedback. I’m anxious to figure out what is going on.
Can you please perform the same serial log test on another remote? I’m curious to see if you get consistent results from another remote or not. That might help narrow down whether you need a new IR receiver (LED board) or a new remote control. Given that you’re getting flaky results from the stock remote — but consistently flaky — I’m now wondering if the remote you got was possibly mis-programmed at the factory or something. Pressing POWR or MENU should definitely never give you the NEXT code.
EDIT: Maybe I misunderstood you?…. You said:
So usually, If i press any button on the remote, I get “IR Code: 2155831455” (NEXT) then “IR code: 4294967295” (0xFFFFFFFF) repeated about 4 or 5 times a second, until I release the button.
Does this mean you get the NEXT code when you hit any button, or is the the behavior when you hit the NEXT button specifically? If so, this would be the correct behavior. 0xFFFFFFFFF is always repeated on NEC-compatible remotes until the button is released.