Plex Client issue: Unknown metadata type: folder

According to this post, this error is safe to ignore. It is apparently related to some development work being done.

This thread has been marked as solved for more than six months and the title is not related to the actual problem the user was experiencing (one of their users was unable to access one of their libraries). You may be better served by starting a new thread and describing, in detail, the actual problem you’re experiencing.