Users on child domain cannot login when connection drop

Hi

We have a situation in our network. An IT Guy that not available either configured a child domain for one our office that this office have unstable connection over a PtP wireless link.

Now , when the connection between headquarter and this office drop , nobody can login to child domain at that office and everything goes to lock-down. I haven't any idea to diagnose this problem because all other sites that configured by me is OK!