The UK has two sleeper train services- the Caledonian Sleeper from London to Scotland, and the Night Riviera from London to Cornwall.
At one stage, the Caledonian Sleeper stopped selling seats and would only sell sleeper berths (because of coronavirus) while the Night Riviera stopped selling sleeper berths and would only sell seats (for the same reason).
While I understand stopping selling seats, the decision to not sell sleeper berths probably has more to do with cost than protection from the virus. See also Eurostar's short-lived decision to stop offering free Wi-Fi in standard class!
It does not run through Prague. It runs through Poland and then crosses CZ from Ostrava to Břeclav. Then SK (Kúty, Bratislava, Štúrovo) and then HU.
Actually in central Europe the night trains usually join and split at some stations, so in Ostrava two trains join: from Berlin and from Warsaw. Then in Břeclav they split again (two halves from each half), one goes to Vienna, another to Budapest. So at the beginning there are two parts on each train and you have to choose the right one. But since the places have to be reserved, you cannot get on the wrong half.
Why is it suspended?
(I'm surprised, though, that the train would pass through five countries. AFAIK it doesn't pass through the Czech Republic.)
The only thing that changed a few years ago is Prague. Changed for SW Poland.