When attempting to log into a multiplayer server on Minecraft, the game will ping the server, showing the message and the maximum player capacity, however when attempting to join the server, an error message will appear claiming that the player is not signed into their Minecraft account. This will appear even if you are signed in or have restarted the game, however Realms work normally.

How to reproduce:

Open Minecraft and log into a multiplayer server. The server I was logging into was spawning.co. The error message pictured below should appear.

Result:

An error message appears claiming that the player is not signed in and suggests restarting the game, however that does not work.