[Miller]

Can they still be fought?

I'm pretty sure, yes. The unresponsiveness isn't necessarily a bug I believe, but the fact you can trigger said unresponsiveness by going down stairs when encountering a mob is.

I'm pretty sure it'll fix itself by exiting the area and reentering.

The unresponsiveness is probably one of Dev's way of reducing lag, since their 'AI' is off until someone actually goes into said instance once.