I resubscribed to Apple Music after a month and all my music is gone

AFTER NOT HAVING IT FOR A MONTH

In the legal documents: Legal - Apple Media Services - Apple you will find, "When your Paid Subscription to any Service ends, you will lose access to any functionality or Content of that Service that requires a Paid Subscription."

That means if you do not have an active subscription, as you did for a month, then everything associated with it such as playlists is lost.

If you stop subscribing to Apple Music, I believe that all of your offline listening copies of Apple Music streaming songs stop working and go away. Restart the subscription and – well, they're gone. The new subscription might let you access the songs again, but I don't think it will restore everything you had set up locally when you ended the old subscription.

Ending an Apple Music subscription shouldn't affect purchased music – songs imported from your CDs or purchased from the iTunes Store, etc. But If you had iCloud Music Library, iTunes Match, or Apple Music's Sync Library turned on, I'm not sure what actually happens.

When you cancel Apple Music or let your subscription lapse, then any playlists created or songs that were downloaded are removed. You will need to download the songs again and create new playlists.