For every game I bought in recent weeks, none of them have the IN LIBRARY tag applied to them, so they still show up in sales lists as Games You Don't Own and while browsing through all releases, they don't have the gray tag on top of the game's banner.
All my previous purchases have the IN LIBRARY tag as always, it's just the recent ones that are glitchy.
And the issue happens both on Galaxy and on browser.

Anyone else having this problem or knows how to solve it?

Yes and No I don't know how to fix it!

Yes, I even had to check my library on one game that I wasn't entirely sure I got in the last sale. To fix it, presumably open a ticket with gog, rather than posting on the forum. I'm too lazy, myself.

GOG is already aware of the problem, but - as you probably know - it takes time for their best people to get things fixed (without breaking a dozen other things, while doing so).

Nope, everything is fine on my end.

Sure it is broken for me too but this is pretty normal for this website.

Is it even confirmed that this is a bug? I noticed it the other day when huntng through the catalogue, and just assumed that it was another thing that was removed because it was too useful -- like the "In Dev" flag on games tiles.

Yeah. I guess technically what was asked there was about a related bug, but I'd say the cause is the same, that only being a symptom of it.

Hmm. Well, that's a good sign, I suppose.

I'm getting the "In Library" notice on Chrome, Edge and Opera across the whole website. Maybe it's an issue with Firefox or its derivatives?

Could be. Site doesn't load in IE well enough for me to even log in to compare, and I don't have any other browsers installed.

Nope, works with no-longer supported version of Firefox.

Having "In Library" tags for games purchased less recently, but not for games in "recent weeks" (actually just the last week for me) does not sound like a browser-specific issue to me.

Edit: "In Library" is now showing up for one (and only one) of the games I recently purchased. Not even the other game I got at the same time. Maybe this means it's being worked on. Maybe it means that only that game will end up being fixed, because it is popular.

So, after reading your comments, I tried to log in through another browser (my main one is Firefox, this time I tried Chrome). And, well, none of the games show the IN LIBRARY tag. None at all.

Well, and thanks for the link regarding the error.
Glad to know it's not a problem on my end.
I appreciate all the replies, guys.

No. I use firefox (latest version), and I do not have this problem. Everything works fine.