I opened Borderlands 3 today (10/11/2019), and to my horror I did not see my level 50 Zane anywhere. Instead, I saw a level 2 Fl4k. To be clear, I had not played Fl4k at all before. I tried to reload the game and signed out my account couple times just to make sure that I was not hallucinating, but all I can see was the level 2 Fl4k. I am not sure if I got hacked, or it is a technical issue. All I know is that 50+ hours of progress is now gone. Let my mistake be your lesson. Make a copy of your save file.
Use the windows feature to restore the save folder to a previous version. It solved and saved my level 33 char when my save and temp save file got both corrupted. Give it a try.
I had the same problem. I tried using the windows restore feature m0l3m4n suggested but it didn’t have a previous version. However if you go into C:\Users\accountname\AppData\Local\EpicGamesLauncher\Saved\Saves
It should have auto backed up your saves, so just copy them from there into
C:\Users\accountname\Documents\My Games\Borderlands 3\Saved\SaveGames