Specific spotify playlists Reddit

This is the second week in a row this has happened to me, I get like 2/3 of the way through my Discover Weekly and then the songs suddenly update to mostly new ones [but still a few from the previous list]. Its not last weeks playlist updating to this weeks, because I check it and listen to it religiously every week- it just seems to change its mind on what it recommended to me midway through. What gives?