For three months now, I've had this same problem. Even the email conversations with the staff hasn't solve this problem. One of lists is very popular and gets new subscribers every hour. But the follower count has been stuck around same number for months now. I just don't get it. What could cause this?
Re: Playlist subscribers / followers count not updating
I too had this problem for a little over one week now, and I FINALLY found the soultion to the problem.
See, what I often do to keep my playlists organized is file them under sub-folders by using the desktop version of Spotify. For example: I have top picks that I create for each month of the year, and throw them in to a sub folder titled "Top Picks", in it, is every month from January to October of this year. Well, that's all fine and dandy, however it creates a glitch; what happens, is that if you keep your playlist in a sub-folder, you'll get a notification saying "you have a new subscriber" when someone decides to follow the playlist, however, your count WILL NOT go up. So for the past week, I've had 3 new subscribers, yet all three of the playlists still read 0.
How to fix: Simply take the public playlist with which you desire the count to go up on, out of the sub folder. By doing this it should resolve the issue, and you're follower count will go up. The reason I know, is because I tested it, using someone else's phone.