Yes predictable, but
DCL do not do anything about it, your usual Caribbean cruise isn't usually full by the time shore trips open up, these panama crossings are full, and many are repeat cruisers so many book at 90 days far more than other cruises.
On the 2005 Panama crossing there was 1750 repeat cruisers, and the system crashed on the day, in fact it went back to telephones at one point as they recently opened up on-line booking.
The servers it seems can cope with usual traffic, but they cannot cope with increased requests at this level, now maybe it isn't worth the cost of having extra servers on standby for the occasional peak, if thats the case, DCL, should stagger the release more, maybe Palo at 90 days and shore trips at 89 days.
We have also seen this on the release of special cruise bookings such as this cruise, so they havent fixed it as yet.
The good news is people were able to book a lot, later, the cruise is very long, so there are plenty of Palo days, that helps, and of course you can book if you get on early in port, on the ship.