Hi cbuck718,
Welcome to Apple Support Communities. I understand that a created music playlist in Apple Music is disappearing unexpectedly after a few minutes. I'll be happy to help.
If you haven't tried yet, I suggest restarting your Mac to test and see if you're able to create your music playlist without it disappearing. In addition, I recommend making sure that your Mac is fully updated to the latest macOS version. This help provide software improvements that can help. Here's how to update the software on your Mac: How to update the software on your Mac
If that doesn't help, the next step is to create a test user account on your Mac and open the Music app or iTunes, depending on the macOS software version you're currently on. Then attempt to create the music playlist in Apple Music to see if the songs continue to disappear. Here's how to create a test user account on your Mac: How to test an issue in another user account on your Mac To help sign in for Apple Music, you can follow the steps here: Manage your Apple Music subscription
Kind regards.