Ann: FDA Notifies Clinical Data Sufficient for Refiling aGVHD BLA, page-863

I am as bemused as you are, @stockrock - especially so because it was announced so soon after a very dilutive CR.

Perhaps there is an unwritten rule that says American ownership must be at least x% before approval can be given.
Perhaps GG realised that back pain was never going to progress until GVHD was set for approval, so he made his move and then told both MSB and the FDA to pull their collective fingers out.
Perhaps the FDA recognise a potential presidential change in November, and realised they want GVHD resolved before then.
Perhaps Si got some dirt on the FDA head honchos and threatened to expose them.

One thing I am pretty sure of. It was neither a scientific nor a clinical reason for the about turn.
As always, shame on you, FDA.