UUID issue

I have a problem with UUIDs.

I've got a server network with spigot and bungeecord, but it's a normal survival server, just for me and friends. The servers are in offline mode (has to be turned off for bungeecord)
I changed my ingamename 2 weeks ago
My inventory and my stats (like how much blocks farmed etc.) were cleared when I logged in afterwards
In the usercache there is a new "user" registered with my new name and a new UUID.

When I go into the Singleplayer files, there is a third UUID for me.

This error occurred in 1.15.1 to me, but I'm not sure if that matters

I'd appreciate some help