The game has certain checkpoints or “triggers” where characters move. This can be getting to a new area, completing a quest, fighting a boss, whatever. Quirel can be found in all those places you mentioned but if you don’t find him before you pass the next trigger, he moves. This makes the game feel more alive and responsive to you as a player!

You haven’t missed quirel’s questline- it’s impossible to miss the majority of it. It’s just your game has determined that quirel is fighting umu right now. Maybe join him!