"What happens to my track licenses if I downgrade? ... the Premium Plan monetization license will expire upon next pay period and the tracks will no longer be covered by this license. Should you wish to continue monetizing without having an active Premium Plan you will need to purchase the copyright for that track."

Oof. So if you use this stuff on your YouTube/Twitch stream, you're locking yourself into a membership with them forever, or else you have to delete your old recordings.