Some friends and I play on a Realm, and we have a some of our player heads around the place. Sometimes, these player heads have the right skin applied, but often, it displays the wrong version. For instance, sometimes copies of my head will revert to a skin I haven't used in over a year (Example: https://i.imgur.com/bh1a3Vn.png and a friend who had the same issue: https://i.imgur.com/8NKdO69.png )
I think this has been happening since we started playing in 1.14 snapshots, but I can't say for certain.