Constantly having to start over

On 2016-12-16 03:09:41 ｜ Show this Author Only ｜ Descending Order

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So this has happened to me twice already and I want to know if this has happened to other people and possibally get some help. I would start up the game, and I would have to pick a character to play again, and all my progress would reset and I would need to do everything all over again. The first time it happened, I was level 6 or 7, so it wasn't that big a deal.But now it reset all my progress with a level 30 character. Can someone please explain to me why or how this happened, and how/if I can fix this?