Xbox one original phantom on off

Hi guys from UK.
I’m kinda of an amateur/pro well I can fix most basic things with games consoles including some microsoldering trace repair etc (still learning alot).
I need help! If I may.
I have a customer with an original Xbox One (black fat one) 1540.
With a what I call phantom pressing on/off issue.
When powers plugged in it beeps and turns on, then beeps like reset has been pressed then beeps to turn off then it keeps doing these phantom presses.
Now I’ve changed the front panel flex cable, I’ve resoldered(reflowed) the main ribbon cable connecter, also changed the actual front panel board and also made sure the main panel connector has a good solder connection and also changed the complate front of the console too.
It was in for a hard drive upgrade too which managed to do. But still it’s doing these phantom presses.
Could anyone help me out on this very strange issue please (I cannot find anything on this on the Internet) so I believe I have the first one that does this.