If the bot is playing music and has songs queued and is kicked out of the guild, it will be saved with the list of songs it had before being kicked out, this causes that if the bot is added again it already has a list of songs, so if you execute the /play command, instead of starting to play the song it will only add it to the queue, causing it to never enter the voice channel and start playing music.

Quick Solution

Execute /quit to make the bot leave the voice channel and clean up the old queue