Thanks for the post.
Does the issue only occur on iHeartRadio or across other channels installed on your Roku device?
If you haven't tried yet, you can remove the affected channel and then reinstall it. To ensure the process is successful, make sure to restart your device before adding the channel back in. We would recommend doing this from the Settings menu by navigating to Settings > System > Power (If you do not see a Power submenu, skip to the next step.) > System restart.
For detailed instructions, refer to this Support link: How do I resolve channel playback issues?
Let us know how it goes!
All the best,
Roku Forum Moderator