I need help getting precise info about Warden Fly

I'm in Act 1, I accidentally killed the very first one I encountered in Bilewater location. I have visited Hunter's March area and only found Ants for now. I've tried looking for the spot he appears in Greymoor but honestly that mitenest isn't pleasant to tread so I dunno where he'll end up. Apparently the spot I'm told he appears in Deep Docks is behind a door I can't figure out how to open. So my question is, what do they mean by "there's a chance he spawns there?" Does that mean every time you rest at a bench and wander over to that spot, RNG is rolling behind the scenes to determine he'll show up? Do I have to advance the game plot a little more to get more "rolls" for his appearance? Does the one in Bilewater ever randomly return after being killed?

Another guide I read says he only has a chance to appear after connecting pathways up. That makes sense, but what are the requirements? It's vague and it seems I've already met the requirement of "travel to sinner's road and bilewater" to get him to appear elsewhere.

Please help me out, let me know if there's only one of them. I'm afraid I have to nuke 16 hours of playing and doing item collection just to roll back to the nearest checkpoint and not kill this sucker.