The last appeals court refused to stay the subpoena and gave him a deadline of May 28 to get the Supreme Court to agree to hear the case.
Miller is supposed to testify about Stone and Wikileaks. There appear to be a number of new charges that could be made against Stone, which would explain why Miller's testimony didn't become unnecessary after Stone was indicted.
https://www.courtlistener.com/docket/7662166/in-re-grand-jury-investigation/
May 21, 2019
PER CURIAM ORDER [1788877] filed denying motion to stay mandate [1786310-2]. The Clerk is directed to issue the mandate on May 28, 2019. Before Judges: Henderson, Rogers and Srinivasan. [18-3052] [Entered: 05/21/2019 06:47 PM]
This other tweet is about his earlier lawsuit (which he lost), but I'm posting it because his picture is here. He looks like he's a teenager.