I've been having this issue since 1.16 first dropped in June. Before that, no issues whatsoever, but as soon as the new version dropped, I was immediately unable to add new skins to my library. There have been numerous reports about this issue, but what strikes me is the fact that per the listing above, there's not even a developer assigned to this, even though in the comment thread a (presumably) developer claims they are aware and working on it. It would seem that if this was being worked on, there would be a name in the "Assignee" field.
The problem persisted after I reinstalled Windows 10 on my machine in mid-July, but strangely enough, my son's new system which never had the game on it previously isn't currently experiencing the issue. Deleting and reinstalling the game on my system has had no effect, regardless of whether I try before or after restoring backups of my old worlds. It would be fantastic if somebody actually took a look into this.
Tried it out on my system and whatever automatic update was pushed seems to have fixed the issue. Finally! Thank you!