An update on this: we’ve been investigating an issue with Garmin’s newer devices that have a “dual pairing” function. From our understanding, some of their newer sensors can broadcast to two apps/head units over Bluetooth simultaneously. It seems these devices can get in a state where they report null (–) values. This was happening on our older apps and it appears to be happening in the new version as well.
Based on other athletes experiencing this issue on other 3rd party apps, we don’t think this is an issue with TrainerRoad.
The support team (support@trainerroad.com) is still a great place to start with troubleshooting, but a good preliminary step is to double-check that your HR device isn’t paired to any other apps/head units (even though it’s supposed to be able to broadcast to 2). It could be worth physically moving to an area where other potential pairings would be impossible, and could be worth testing the TR app on another device too.