Ann: Trading Halt, page-379

My opinion;

Early trade on NASDAQ - MESO - trading halt.

FDA contacted MSB. We don't know the details, but we can presume it was sensitive enough to request TH.

9 hours later, TH on the ASX.

It's fair to say the FDA is in discussion with MSB regarding details of Ryoncil.

Bottom line is, it's close to approval with a few conditions that need to be ironed out.
If it was not to be approved, you don't need 1-4 days to prepare a letter of CRL.

Also, when a CRL is recommended and announced to market, the company arranges to meet with the FDA to discuss the process to get the product approved.

Also, I don't believe the FDA has given MSB a heads up regarding date announcement. There is more to it, thus my opinion above.