All my companions are gone, and I can't go back to Act 1 & 2 areas.

[Kayla]

TLDR:
All companions not in current party dissappeared from camp when i entered act 3, and now i have no clue if they can be recovered or if my game is bugged for the rest of the playthrough. pls halp.

Wall of text:
Towards the end of act 2 moving in to act 3 i realized that all my companions that were not currently in my party had just up and vanished from camp. The only playable character other than my party moving into act 3 seems to be Halsin. And he becomes a companion as a result of moving into act 3... so ... well...

At first i thought this was a "feature", and that because of my actions in act 2 regarding those characters and/or the lack of me pursuing their story archs had led them to just abandon me.

However, I have now met multiple NPCs in act 3 who refers to my lost companions with lines like"Talk to them in camp" , or "Bring companion X, and then we'll talk" et.c. This has led me to the conclusion that this is a MAJOR bug.... Has anyone had the same experience?

Can it be fixed without rolling back half of my current play time?

I also cannot travel back to any area from act 1 or act 2 after entering act 3. Is this also a bug? I read somewhere that one is supposed to be able to return to previous acts to see how things have progressed and changed based on my previous actions... this could be a lie though.... But i also read somewhere that companions could get "stuck in indoor camps in dungeons" and thats why they might disappear from camp.... and that one can go back to previous dungeon camp locations and they might appear there again. This i cannot try because i cannot return to act 1 and 2 areas, and all my companions were gone in act 3.

[Hawke]

If I remember correctly, most companions abandon the party if their quests are not completed in Act 2. There is also a small transitional area between acts where you auto-camp, but I think the benched companions should be available there.

Just in case, after the Nightsong has been dealt with, returning to the previous areas is not possible.

I would suggest to do hard saves before the point of no-return (the Shadowfell) and before the bug became obvious, then to try to continue. If the companions do not return upon entering the city's outskirts (providing that their quests have been completed), something is definitely off.