As of 2024 I have a similar case. Inventory reset and exp reset, completely seen as a different player with the lan icon. Me and my girlfriend play on a world (bedrock edition of course) and we, one day, log in (it was around 10 days ago and the entirety of her inventory and exp was completely gone. Not only that but she spawned at the world spawn and i was seeing her with a completely different skin than the one she was seeing herself as. I spoke with the help center via email and said to write here cause they couldn't do anything. So i wrote a post in here (MCPE-186526) but the team updated it as resolved and nominated it as a duplicate of this one.
I hope that, even though it's a year later, they are still considering this problem and not just straight don't care about it anymore. For any more info that I may have forgotten just ask.
I mean, it literally is not the same. While the inventory gets wiped clean and the exp is gone in either problems. My problem is much more straightforward. She is seen as a second player, always in lan and there is no reverting back from that. They all have a problem with the player saves but none of them says anything about being seen as a different player. I'll post under that post as well (and it's a year old so i hope you are still considering it).
still a problem in 1.21.1
logged in a world that we used to play online while we were playing locally (so loaded it as lan) and as the second player joined his inventory was completely wiped clean. I already reported this problem in like 4 different places. This is becoming a nuisance because everytime the second player joins his inventory COULD be reset and i'd have to grind everything back again for the second player. It's the second time now this has happened.