Xbox One games won't start, but Xbox 360 ones will

Hello,

I have a Xbox One S All Digital Edition.

I have both retro compatibility games (Xbox 360) and Xbox One games. The Xbox 360 games work just fine, but the Xbox One games don't. Some of them will give the "game took too long to start" message, others will load the the game but will take too long to
start a new game or load a save (too long as in more than 10 minutes - I didn't stick around to actually see if it eventually loads), others will load a save but the game will freeze or suffer stutters or even fail the sound constantly. I tried to restart
the game, restart the Xbox One, turn off the Xbox One and remove the power cable for a few minutes then turning it back on, reinstalling the game, resetting the Xbox One to factory settings (and tried both options - the one that erases the games and app and
the one that doesn't). Then I was put into contact to an expert gamer in the Xbox website. We went through other solutions, like resetting connection settings but nothing worked. He then told me to request a repair from Microsoft because this might be a hardware
issue.

And I said that Xbox 360 games work fine, right? But if I try to start a Xbox One game and it eventually fails and then I try to start the Xbox 360 game, it will fail. If I restart the console, the Xbox 360 game will start normally again.

And while all these problems are happening, the Xbox One itself will get slow (usually when leaving the games).

I'm posting this because I haven't seen a similar problem (360 games working but One games not), and I've been surfing the web for almost a week now trying to find a solution.

Did anyone go though something similar? What did you do to solve it?

:)