This happened to me Friday 4/21. Thursday I tried to check in online. The system got to showing the seat assignment step and failed but I could click forward. Then it just crapped out with a message saying it was Jetblue's fault not mine (some such happy-go-lucky message that did not mean anything). I tried different browsers, on my phone even and got the same experience. Tried the chat and calling got the same answer can only check in at the airport not over chat/phone etc.

Went to JFK arrive 90 minutes before boarding not even the flight time, tried the Kiosk, and got the same experience of not being able to show the seat map, and then the next step it failing completely. No staff at the kiosk so went over to a line with a large number of people with bags. The uniformed line minder insisted that I had to stand in the line for a gate agent. Even insisting that I had no bags to check and it was Jetblue's fault I couldn't check-in.
Left wife in the line and tried to find another employee, went to the front of the line but that same line minder ran me down and physically blocked me, and insisted I had to wait in line.

I got to the counter they couldn't even check me in at the counter. The person claimed she was getting an error, then said it was too late for me to even get thru security even though we have Pre. She had to call someone to get us on the next available flight 7 hours later, that call from one JB person to the other took over 15 minutes to process.

My return flight was on a different PNR and that had no issue well issue with checking in. Though the flight took a 7-hour mechanical on an E190 a part had to be flown in. Our 10a flight the inbound metal they gave to the 6a flight that the plane was sitting overnight with the issue we would get since 6a was already waiting 4 hours. Of course, the next E190 arrival we didn't get a swap and had to wait out the repair (no seats until 10p flight unless I wanted to go to HPN).
The JetBlue experience!!!