Thanks, KokoCollino! In that case, revenue really seems to be the answer to the problem. Gzuz must have sold a lot of deluxe editions of his album. Same for Lina, who , according to Amazon, had a box set that costs more than 40€. This way, she could land ahead of Gaga and Cooper, although I have her sales at ~ 40k and Gaga/Cooper's sales at ~ 150k. This time around, the revenue system 'disfavored' Gaga/Cooper because their album has been placed higher on the sales-based chart than on the official gross-based chart for most of its charting weeks so far.
There are even more extreme cases than Gaga/Cooper though: Acts like Andreas Gabalier or Santiano regularly have their catalogue albums' certifications updated, despite their albums only charting in the lower parts of the charts (or maybe not even that), because they are heavily discounted and so sell a lot of copies for a low price. 'Bis ans Ende der Welt' probably sold 60k+ copies in 2018 - and its last charting week was in the last week of 2017.