Ok here is something I tried hope it could shed some light on what is happening.
I connected my laptop to an old LCD screen and a 42" TV screen, the game worked perfectly even on the laptop screen. On the LCD screen it was mirrored, so I got 2 perfectly adjusted game screens on both. When I plugged it to the TV I only got the game on my laptop screen but also perfect resolution (I think the difference between both screens was I used different ports, HDMI and thunderbolt, and each having different settings)
Do you think this would help?
UPDATE:
Plugging the screen, running the game (it runs well), then unplugging the screen would keep the game in the right resolution.
Trying to run it again without a screen gives the same problem as before