I completed ACT 1, 2, & 3 and received the reward for completing all 3 Acts. When I went in just now to start Act 4, I noticed that it’s showing Act 1-5 needs to be completed. It literally wiped out all my work? What am I doing wrong?
This is how Adventure mode is intended to work. Unlike the story mode, you are not completing a set of objectives which remain consistent over time. Adventure mode provides a new set of bounties per act every time you play. For a more story-based experience where you complete acts over time with consistent progress, you would need to be playing campaign mode.
You can read more about the various modes on the Diablo 3 website.