I went from Level 19 to Level 3 yesterday after a match. I still got the xp from the match, but I lost all other progress. I also lost the cosmetic items that I had unlocked. I'm able to keep wearing the items that I had on before the progression loss, but they come up as needing to be purchased in the customization screen now.

That still hasn't changed?
I had this happening for me too. But not from Lvl. 19 down to Lvl. 3.
More like from Lvl. 13 down to Lvl. 12 but after like 1-2 hours of gameplay it showed me the right level again. I think it just has some problems with tracking your progress and sometimes gets confused. But I bet in the background it saves the right "settings"