Looks like other users with other devices are having the same issue.
Best to add your issues there by tagging the member of NOW staff who is trying to help to see if there is indeed an issue.
I own a BT DTR4000 Youview box and i have just checked the NOW App on it and the Watchlist and Continue Watching grid rows are still there.
I can also watch stuff on both the Continue Watching and Watchlist, plus add new content to my Watchlist on the Youview box NOW App and view & watch it.
It seems a strange one this, because not all owners of the devices reported seem to be having the issue and i don't think it's an account related glitch, because it would affect all your devices i would guess.
If it was more widespread i would have thought there would be hundreds of reports on the Community Forum.
Hopefully the NOW Tech Team will get to the bottom of this.