This kind of thing is quite common once Pi-hole is blocking domains. I see the same on some embedded video – the player loads but the content can't load and the player is just a sort of shell. That's because the player loads as part of the app or site, but the content for the player typically comes from a content delivery network somewhere else; these often have "cdn" in their domain names. Pi-hole may be blocking this, and hence you just get the empty player.
What happens next depends on how the app or site deals with that. It may freeze up waiting for content that never arrives, or it may try to play the next item, then the next, just skipping through a bunch of titles that don't work.
Here's a post from the Pi-hole Reddit where someone posted a load of whitelist and blacklist domains for Pandora radio. It may be worth a play with, but it is 4 years old so probably of limited use.
You may have to find where the content is coming from, and create a fake domain entry so it resolves to something, so the Pandora app "thinks" it's merely broken rather than unreachable, and this might be enough to stop it freezing. Your Query Log will help you see what's blocked and what's getting through. This post gets quoted a lot and may help.
But it may be that the current version of the Pandora app simply cannot deal with advert content being blocked and sits there waiting, locking everything up.