GIVE UP. HELPFUL INSTRUCTIONS FROM US ARE IGNORED.
Quite offensive statement. :P
I think, you are supposed to press "add XP", then kick a zombie in the balls, therefore gain "real" XP and then trigger the real level up.
If you just smash the "add level" button, it will only increase the numeric level but not the real ingame level.
I remember hitting the add XP button all the time, run around, kill some zombies and thus get a proper level up in the main game.
And I also guess, we are running out of keys.
No offence intended and you basically just repeated what I wrote. Add xp, hit a zombie or drive 2 meters and you gain a level. That's how it works. 'Add level' causes problems because the upgrade system sometimes doesn't recognize the level gain. That's why you could basically pull the 'add level' option.
Thanks for the link btw but it doesn't always translate like that. Had to backup save, test the keys and restore save.
The current trainer works fine with Dying light + the following DLC. The enhanced edition is a patch that has been applied to anyone owning dying light regardless of the DLC.