Incorrect Number of Authorized Devices

Apple Music keeps telling me I can't authorize more than 5 devices, but when I go to my account settings I only have 4 devices authorized.

I'm trying to play a song that's been in my music library for years, but Apple Music keeps telling me first that I need to authorize it, then when I do that I can't have more than 5 authorized devices. However, when I go to my account to deauthorize an old device, I only have 4. Why is it telling me I have 5?