I was looking at the 22nd, which still shows up on journey planner, realtimetrains, etc, and you can in theory purchase a ticket for it it looks like, but on phoning gwr i'm told its seated only with no sleeper berths available.
The night riveria page says to phone to book berths. I can't find any mention of it on the "paper" timetables page, (or indeed any dedicated london to cornwall paper timetable any more??)
The engineering works page says nothing about it stopping, nor does the coronavirus page.
I tend to agree with broadgage, closure by stealth. maybe it only serves
GWR▸ to run it in peak summer holiday season to catch the holiday crowds now? Whats next, overnight bus replacement service from cornwall to london?
When GWR say "due to a problem with our reservations system" I'd love to know what that actually means. And when the advisor said to me the cancellation has "only just happened", I wonder when exactly management decided this...