The Sync Library button will turn itself on on Apple Music on my Mac

I have thousands of CDs that I have imported into Apple Music on my Mac over several years. So I have the Sync Library button turned off so I can listen to the CDs that I have imported. I do this because I believe that there is a limit of 100,000 songs you can have in your music library. I have also created many different playlists so that I can pick what playlists I want to listen to. I use these playlists on my iPhone so I do not have the Sync Library checked on my phone.

The problem I am having is that every once in a while when I reboot my Mac, the Sync Library button will be checked when I bring up Apple Music. This wipes out all of the music that I have imported into Apple Music. It also wipes out all of the playlists that I have created and the counts of the songs. I have to turn off the Sync Library button and import all of the music back into Apple Music from the external drive where I store my music. And I have to create all of the playlists again. It is a real pain.

My question is why does the Sync Library button get checked without me manually doing it and how do I keep it from happening again? I purchased my iMac in 2014 so it is an older computer. I don't know if that is part of the problem or not.