Strange. I had a similar problem - I had played episode 4 for a while and when I wanted to continue at another session, it suddenly started with episode 1. After following the sticky thread instructions I could at least restart ep4 with the choices from the previous episodes intact. After quitting the game via the menu I have also been able to continue the episode twice.
I guess I was halfway through after the wipe of my save and it sure is annoying. There should have definitely been some warning, maybe a popup message when starting the game as soon as Telltale found out. (Not mentioning that this should never have happened, Q&A definitely fucked up).
So maybe try the instructions in the sticky. I had to redo them twice I think until it worked.