I know it may sound silly and childish but I've reinstalled The Witcher 3 and noted I lost all my past achievements, meaning they don't show on GOG Galaxy anymore. Anyone knows how to fix this?

if you have all the dls for the game you would have 2 versions of the game within your library the game of the year edition and the regular edition but the achievements are independent of each other

Yep, I had a "The Wither 3 Wild Hunt" folder in C:\GOG Galaxy and another one inside the Program Files folder. Since I kept only the first one this time, I think that's the problem. Thanks for the info!

Same problem here.
How can I play my old game 68hours played?
If I try both version games I must star from zero,no savegame to charge...