https://www.huffingtonpost.com/entry/robert-mueller-interview-trump_us_5c147594e4b05d7e5d82235e
Here’s the link to the story fro HuffPo on Mueller seeking to interview trump. If trump is resisting a GJ subpoena I can see the court taking these measures to keep it from becoming a media circus while the decision is made. The law is pretty clear that the President can be subpoenaed (Nixon and Clinton). But I can see the kind of effort being made would only be made to keep someone of this magnitude secret.
I don’t think it has to do with moving Butina – the request made under seal should have been kept secret of course but the clearing the entire building so that the identity of the lawyers and who they represent would not be done for someone like a Butina. The only one who makes “sense” is Trump himself.