I thought i had the same issue once and that I had lost about 10+ hours ( I know hardly compares to 7 playthroughs ) but it was the game loading an old save. Once I manually loaded i was right back where I should have been.
One feature I would have loved is a more manual save system to avoid situations such as this.
Wasn't a glitch. Apparently my save data got corrupted and that was all that was left. Or something? I dunno but yeah it was all gone.
I really like the underground locations of the game. The caves, catacombs, water altar or whatever, etc. They are very well designed. Still busy with 1st playthrough, lvl 32 archer. Said it before, I'll say it again.. Great game!