try to re sync

Have you added a game since? if not add a free to play game then re-sync then you can delete the game

Try removing it from your steam WL and synch here, then re-add it to steam WL and synch here again.

Try check hidden list

Has not happened that I'm aware of. As a test. This game is not on my wishlist so I added it. It now show in my WL search. I removed it again and it gone again. So its working properly for me. This does not help but it does say its not a problem with this particular game. I don't know what would cause this but it must be something related to your account.

Try logging out completely from both here and steam. Then come back in and try again. Perhaps the cookie itself is corrupt. You could try and remove your steamgift related cookies and see if that helps. I'd remove all steam related ones as well just in case.

Might be a browser issue. Try the others. If its a browser issue then perhaps its a plugin your using. Try without any enabled and add them back in till you find the issue.

If none of that helps then it might be time to log a ticket with support and see if they have any suggestions.

Oh only game Im aware of never shows in wishlist section is sam & max which i completely forget about until i see it and im like oh yh i need to keep checking. So i get how annoying it must be especially if youve had it for like a year