Do you select songs manually and put them into iTunes playlists? Also, do you sync the lists (from time to time) between devices such as from an iPhone to a Windows PC or vice-versa? (Although it shouldn’t be necessary to sync devices in the first place as nowadays both are able to connect to the cloud, isn’t it so Apple?)
Then you are like me. And maybe also like me, you might have noticed that sometimes some playlists appear to have less items on the phone than when displaying the same list on your computer (even if you check under the synced device). And sometimes syncing the devices after some time you might even get list duplicates, having “1” postfix, e.g. if you purchase a new item on the phone and add it to an incomplete list there, then sync.
I have researched about this and although no one seems to know the reason of this bug, it seems KKC1969 has found a workaround! The issue seems to occur only if you haven’t played the songs after purchasing (on the computer), so their play count is zero in the iTunes library. I have checked recently, and if I just played the new songs (for a minimum of around 10 seconds!) on the computer and syncing the playlist between the devices again, the counts of songs were equal again! Hooray!