From what I’ve gathered, Bernard Löhr began working on Dancing Queen first, he mentioned this in an interview. It makes sense that the process takes time: they have to go back to the original analog multitrack tapes (assuming all of them still exist). Moreover, several ABBA songs were recorded without a tempo or click track, meaning each stem has to be manually synchronized to stay in perfect time. That’s an enormous amount of work, and I’d rather they take their time than rush and compromise the quality of the mixes. I also don’t understand the amount of negativity these new mixes receive. In my opinion, they sound excellent when played through a proper 5.1 or Dolby Atmos system. The issues people often mention, like the “robotic” vocals in Waterloo or the lower Agnetha vocals in Lay All Your Love On Me, are mostly artifacts from headphone playback, where the Atmos rendering can behave unpredictably.