This just started happening to me yesterday. There are a good number of videos demonstrating this by a lot of people. After i get booted from the server, if i rejoin, all progress on weapons and unlocks is zero.
:Repaired game files and nothing. Now i'm running around on the only BF1 server active at the moment with base weapons because the server thinks i'm lvl 0. Server has 2 slots open for airplanes. Someone will try and grab a plane, they'll get booted. Server realizes no one is in a plane so the available plane count shoots back up to 2 within a moment or two.
Played as a scout and went to whip out K bullets and for some reason, instead of K bullets, i got some short barreled lever action gun with no iron sights. I thought it was rather odd...... The icon for that weapon slot even says K bullets.... yet i whip out a 3rd gun???