Why is my player loading as "unknown" in testing mode?

I have a big problem, every time I test my game, I join as a player with a username "unknown", and a display name "unknown+DN" and my avatar is a noob, here is a screenshot with some details: https://ibb.co/LSN2GRc (paste in google search bar)

I have some data store issues because of this problem (The data store always resets and other stuff happens), and it needs to be solved. Maybe the game loads a player "unknown" because of my internet connection?

Also, I have a music playlist that constantly plays a list of music, and sometimes the second track mixes with the first one, I found out, that's because the first track doesn't load in properly (just like my player or character, which is replaced by "unknown"), and the "length" property of the first track is automatically set to 0 because of that. So the second track waits 0 seconds before starting. So the music mixes up.

All of that because of this "unknown" player that loads instead of mine.

Any help is appreciated, thanks in advance! :D