Can't enable Sync Library, even with iTunes Match subscription.

I reinstalled the music app on my phone recently. I can't get the toggle for Sync Library in the Music preferences to stay on. I have an iTunes Match subscription, and the feature is enabled on my iMac. When I enable it on my iPhone X, it turns green, but nothing happens. If I go back to Settings and then return to the Music preferences, the feature is disabled again. I can't get it to stick. I'm running iOS 13.4. My phone and iMac are logged in using the same Apple Id. When I go to Apple Id → Subscriptions on the iPhone, it says iTunes Match is active.

Has anyone else had trouble with this?