Seems no surprise the issues are partly (mostly?) down to IT. Carnival UK seem to always be in perpetual IT disaster. The old P&O Cruises "My Booking" web app was always a mess, slow and broken. Then they released a new "My Holiday" web app that looks shinier but again seems to be broken most of the the time. Giving you a countdown when entertainment/dining can be booked only for the day to come and when you try it just spits back error messages.
On board the My Holiday app is equally as bad. On Iona recently it was terrible, so slow, and it went down more than once for more than an hour, causing on board chaos as people queuing outside venues and staff not knowing what to do. The ship has WiFi access points everywhere but if you have the app open and move around the ship it cant keep you logged in. So you can be thinking you are in a queue but if you refresh you are just sent back to login page.... despite the web page telling you to 'stay on the page'. If you do though you'll have no idea if you are logged in or if it has logged you out and stopped refreshing.
On Azura earlier in the year the on board My Holiday app seemed to work better, so quite surprised to see it being some how worse on Iona a few weeks ago as a newer ship.
Then theres the WiFi. They offer two packages one for slower speeds and then another "ultimate" package which promises faster speeds and streaming. However.. if you start on the basic and upgrade mid cruise to ultimate... the WiFi speed is exactly the same (ie. very slow). P&O then says "ah it is subject to satellite signal". However it never improved over any of the remaining five days I used it.
Anecdotally I have heard from people who work at Carnival House in Southampton that internally the IT is a disaster also.
They should just get some expert, outside help, or something to help overhaul everything they are doing IT wise and bring it up to an acceptable working standard.