Witcher 3 doesn't show as owned on store page like all my other games??? Any idea why?

Did you purchase a retail copy, it from GOG.com, or via a third party site?

If you purchased a retail copy, firstly make sure you've redeemed the code on the back of the game manual.

Then, if you purchased from GOG.com directly or a retail copy of the game, refresh your GOG account by going to this URL:
https://www.gog.com/user/refresh

If you purchased from a third party and it has also disappeared from your games library too, your serial may have been revoked. In which case you will need to contact the third party seller for a refund.

(I saw a day or so ago someone from GOG.com mention that they had revoked some license keys that were obtained illegitimately by third party sellers, so it may be the case that yours has been if you didn't purchase from GOG directly.)

I have exactly the same problem. The game sits nicely on my shelf and plays nicely on my computer, but if I happen to visit the store page of the game it doesn't show as owned.

However, if I move the game to my shopping basket and try to checkout, I get a warning that the game is included in The Witcher 3 which I already own.

Could this be because I got my game with a code received from buying a GTX 970 card?

Got it all fixed up. I ended up buying the Expansion pass which gave me a copy of the GOTY version. :) All working now.