This is an issue relating to server lag.
I used to play in an EU server regularly, and I’m in America. Whilst my ping was very playable, at peak times for the server there sometimes would be lag and I had several metal doors “float away”. It was quite hilarious the first time I saw it, it literally just flew away like when a child lets go of a balloon.
If you just wait, the lag will catch up and the door will be back there. You can place another door in it’s spot if you want, and you’ll end up with two working doors in that one doorway. Unless it’s a crucial point in your base I’d say save the 200 metal fragments and just wait for the original door to pop back in.