Took 9 down in Feb '19 over 2 days incoming and 1 leaving Jet Blue DCA - SJU - EIS with the last leg being IC. No issues with any of the 3 trips other than long walk to D gate past Margaritaville restaurant. There is a Margaritaville bar just down from IC's D gate to help you pass the time as Jason indicates

Did IC in October '18 no issues. The only change in Feb '19 (DEPARTING EIS to SJU) is that IC took carry on bags at check in instead of having us walk through security with them

We did carry on...

I have not seen them (or Seaborne) close the gate with an hour left even though they say that.

There is a long thread on this connection maybe a month or 2 ago if you search