Repro Steps:

1. Progress through any given Act in Offline Play Mode
2. After completing any given number of quests from the current act, go to town and quit the game
3. Launch the game again, select the same character in Offline play also

Essentially, any quest progress within an act is lost upon reloading the game. So the only way to progress in the game has been to complete each act, without reloading the game.

I've had to edit the JSON save file twice now because I can't always spare the time it takes to complete an entire act in one go.

EDIT: I've noticed sometimes when this happened, I was prompted to reload the game due to a new patch version needing to be installed. Not 100% sure if it happened every time though, so it may be a red herring.

Thank you.