Not sure what happened, but all of a sudden, all the achievements that I've unlocked but were still showing up in grey, now appear as unlocked yay! Even more, all of those that were "secret achievement" are now revealed so.... solved?? Let's see when I unlock my next achievement

Same problem still appears. Many achievements I definitely unlocked (they even showed up in my timeline) appear unlocked in the list and also on external achievement trackers.

Resetting any settings or files from Galaxy did not fix anything because I just got a new computer and all the old ones stayed locked as well as new ones not unlocking