This can happen if you lapse in payment of a prior rental but don't cancel the subscription first before re-renting that same track. (Various things can cause a lapse in payment, including insufficient funds, expired credit card, etc). The system will automatically attempt another payment 10 days later, and if successful, that would cause both subscriptions for the same beat.
The solution is to cancel one of those subscriptions through your orders page so that you only have one subscription per beat. See this article on how to cancel: https://soforeal.zendesk.com/hc/en-us/articles/360023652413-How-do-I-cancel-my-monthly-payments-subscription-for-Exclusive-Rent-