When I click to sort the wishlist by putting discounted games first, the wishlist is sorted seemingly at random.

Discounted games no longer appear in the top spots.

It sorts kinda alfabetical order, but many games that aren't discounted also appears.

The Discounted filter hasn't worked in a long time, and staff are aware.
https://www.gog.com/forum/general/discounted_not_fully_working/post19

It doesn't have anything to do with sorting though. Sorting options are above: Title, Date Added, or User Reviews.

On an unrelated note, AVICII Invector is great. You should get it.

How disappointing. The "wishlist bug" it sounded like something special and magical, like the wishlist fairy - the magical fairy that grants all your special wishes.