I am having this same issue. I noticed it when I stopped leveling up. I also am using game pass version.
That's really odd that you guys are having issues. I'm on the game pass as well. And i just set the xp multiplier to 200 and it boosted me to level 30 in a couple kills along with my companion. Not sure what's causing it on your end. I also had hp, ttd, and durability on. Maybe you guys have to get to a specific part in the game or be near the ship?
Maybe it's because we aren't using the xp multiplier? The only options I was using was infinite health and ttd. I tested it without the trainer and xp was working normally, then I tried it with only the trainer activated and no options turned on and when I would kill something that gave me 400xp it would reset my xp from 3000 to 400, then find a new area for 150xp and it would set my xp to 150. 🤔
Im also on gamepass and having the Same exact thing is happening to me as well. Except im stuck at level 2 instead of level 4. I've tried the same test as Kindred as well.