Hmmm.

EDIT: original post reworked. I was looking the wrong direction

Or it is planned, but full, or there’s uncertainty about the timetable because of Engineering works. Best book a day before or after. 1st of may is in many European countries a public holiday (Labour Day) which might fill up the trains quite fast.

On the website of Nightjet itself I don’t see that connection anyway.

Double checked, I don’t see any availability for April what so ever. There seems to be plenty still in March.I doubt that all Parisians went full exodus on Austria for Skiing holidays or city tripping. :)

Best contact ÖBB to check what’s going on https://www.oebb.at/en/reiseplanung-services/kundenservice or somebody else on this community might now. But I think bookings are just not open yet. Try again in a couple of days/weeks

SNCF is going to open bookings for that period on 25/01, so you could check again then. But I think Nightjet bookings open 2-3 months in advance.

Thank you so much. I’ve sent ÖBB a message and I will also check again on 25/01 if I don’t hear back. 

FYI I have heard back:

After the international timetable change that took place in winter. All the tickets are not updated in our online site and it will take some time. The tickets can be booked in the next few weeks.

FYI I didn’t end up booking but this is open for booking now.