Payment gateway restrictions w/Authorize.net

I am using Woocommerce with Woocommerce Subscriptions.

I enabled ‘mixed checkout’ in Woocommerce > Settings so that customers could add more than one subscription product to their carts.

But when I tested it and tried to add more than one subscription product to my cart, I received the following error: “Due to payment gateway restrictions, different subscription products can not be purchased at the same time.”

This is odd, because I am also using the Woocommerce Authorize.Net CIM Gateway (2.3.2, latest version), which apparently supports multiple subscriptions (see here: https://docs.woocommerce.com/document/subscriptions/payment-gateways/). It’s enabled and worked fine before turning on mixed checkout.

So what’s the problem here and how can I fix it? According to the docs, everything should work. Have I missed changing a setting somewhere on the Dashboard? Or is this actually not possible?

Thanks.