I changed my username at the same time as I had a launcher open, and when i loaded the world, it just set me back to spawn at the start mode, it probably has to do with that it cant verify its me and dosent know how to treat the user.
What happen was i was back at 0 with no inventory and player location info. The commands also didnt work except for things like */list and */help
*=Just there for formatting, it wouldnt let me type the command otherwise.
Environment
Change playername and skin all other things were the same.
Issue found.
I see the issue. Since changing your Minecraft name also gives you a new Unique Player ID, having your world open at the same time made your world think you joined in as a new player. This means it can’t confirm your identity. This is why your permissions are limited and why your at spawn with nothing on you.
Troubleshooting.
The easiest and strongest way i recommend you trying is to first exit Minecraft and the launcher. Then do W+R and enter
%appdata%/.minecraft/saves/<world name>/playerdata/change the world name of course.
You then will (or should) see something like this:
<old UUID>.dat<new UUID>.datYour information will most likely be in the old UUID data. The easiest way to fix this is to either rename old data to new data or just simply delete new data and let the world do its thing!
Hope this helps!!!
-Kuba :)