The issue is not new.
I think the issue is about 1 week old, or even longer.
I am very sure that the issue was there befre the summer sale ends.

Happening here too. Tried to add Northgard to my wishlist but it doesn't work.

I could add it to my wishlist just fine, even though I appeared logged out per top bar. What happens when you try it?

I can't access my profile on the website (500 Internal Server Error) and some collected achievements have disappeared from Galaxy.

Maybe related to that Witcher giveaway since everybody is trying to connect their accounts from Steam, etc...

It didn't work for me in the web browser several times. A half hour or so later I brought up the game's page in Galaxy client and wishlisted it there and it worked though. Checking the game page on the website it still doesn't work but at least they seem aware of it.

Looks like the problem was fixed, at least for me, I'm not having problems anymore... :D

Update:

- Store page glitch appears to have been fixed (visited about six pages), shows logged in.

Not sure if the profile and achievements issues have been fixed that Hustlefan mentioned, since I really don't use those features.