And that is how you learned not to go into a Wildlands until you are ready. They are meant to hunt you down once you enter.

It's a bug. Surely you don't think Stardock intends allowing unkillable stacks of monsters to track you halfway across the map and destroy your empire with nothing you can do about it. I can't think of a faster way to frustrate players and turn them off. I don't think they want folks rage quitting FE the first time they play it.

All you have to do is NOT go into those areas until you think you are ready. It's not like they are hard to avoid.

I'd argue that if intended, it's bad design. Let's say you are a new player early in the game. You think 'let's explore over here' and 'oh no, it's after me'. Fortunately you are faster than the ugly looking pack chasing you so you get away (you think). 30 turns later they show up at your single city and destroy it. Game over.

Now, we have what seems to be one seemingly trivial decision made by the player effectively ending the game. Nothing strategically or tactically they can do about it. There's nothing 'fun' about this. There's no 'interesting decisions' to be made there because nothing you do matters. To boot, exploration is actively discouraged because one wrong step and it's terminal.

So, I can't see how this is possibly intended as part of their design. I think it's far more likely that the AI is just overly aggressive right now or that it isn't releasing targets properly after chasing for a while. If you'll remember, the first beta had a problem very similar to this and they fixed it.