These are some GOGmixes, with more than 10 votes, that appear empty to me, using Firefox and IE:

http://www.gog.com/en/mix/games_with_spanish_languaje
http://www.gog.com/en/mix/gog_adventure_games_in_chronological_order
http://www.gog.com/en/mix/games_with_soundtracks
http://www.gog.com/en/mix/great_pixel_art
http://www.gog.com/en/mix/games_with_bonus_soundtracks

The majority of users probably don't care about it, but I'm sure that at least the creators of those lists would appreciate if someone at GOG could fix them.

It was already mentioned few times earlier. there is a bug that sometimes flushes entire thing on save. Mixes are broken for quite some time, and as far as I recall they are basicaly legacy feature. They are not advertised anywhere and are probably still there as no one bothered to take down that part of site.

^That's a pity, I think some of the lists are quite useful (games that work on linux and mac, for instance). I'd better save the mixes I'm interested in, just in case.

I have stopped updating my GOGmixes, because they kept being emptied on every small update and I had to reenter all the data myself if I wanted to restore them. GOG support told me then that this won't be fixed anytime soon, since they are working on fixing problems with higher priorities, hopefully that will change eventually.