***UPDATE***After a lot of back-and-forth via email and in-app messages, here is the key - create an account if you never had one (I didn’t), then in-app message a new thread (even if you’ve already been without an account), and next patch your list comes back. (As of version 25.8.5) Wish they would just have said this was an account creation mandate. Wasted so much time and effort - why only went from 1 to 3 stars after fix, the pain of it all cost a couple stars (and the “Last added” sort data is now scrambled). Thanks to post “Watchlist Gone (now back!)” by Whatlist? on Jan 22 for an idea on how to fix this after over a month!!!
Same issue apparently many have had. Several versions ago all user data (my watchlists) were deleted during an update. I did not have an account, but it’s always saved my data for years (locally on my phone I’m guessing). I held out hope after contacting support at the email given in developer response to many other reviews, but nothing recovered so far. It’s not looking good, it may never be, and I’m so sad - lost years of history and because I’m not starting over, it will be the end of my using JustWatch :-(