Not sure why DESKTOP-8T2EMTA\ is getting added in the first place then. I did do some testing and noticed that once it started to get added during upgrades, I had to restart my entire system to get it to stop.
Ultimately, for now the best thing to do is to manually set the username so it doesn't include the \u or escape it with an extra \. Or change the user name to not start with u. Then once the fix is in place in a future update, you won't have to worry about it.