This happens because the cloud sync does not sync properly. If you have unlocked everything and quit the game then Steam will upload your save file to the cloud. When for example later you re-start Steam and the game steam will try to download the cloud files but fails then the game will create a new save profile. It can get even more frustrating because the full save file in the cloud was still there (but Steam didn't manage to download it properly) at that moment but when you quit the game it will overwrite your full save with the newly generated save (which is empty) then all progress is lost permanently.
I've had this happen many times over (with multiple PCs there's a lot of save file synching). This is not the fault of RL or Psyonix but rather the stability of the steam cloud.
Ranked Data is stored online (to prevent tampering and allow the Season resets is my guess) and not handled by the steam cloud.
You can Back-up your saves, they should be in the following location:
C:\Users\username\Documents\My Games\Rocket League\TAGame\SaveData\DBE_Production
Hope that helps.

https://www.reddit.com/r/RocketLeagu...ust_restarted/