You’re getting good troubleshooting advice from the HR strap failure perspective, but while this is categorized as a ‘TR Software’ issue and ‘bug’, I should advise that the Forum isn’t the best place to ‘get to the bottom of’ an issue that may be TR software related.
Its super device/version specific, support knows best and is the quickest to provide up-to-date info (and in this instance, the action items to help). 
From the ‘Welcome to the TrainerRoad Forum’ Page:
Have a question about the app, your training plan, or device? Reach out to support@trainerroad.com instead of posting here. Our support team has the best visibility and insight into your devices, workouts and adaptations, and will help get you the most efficient and effective answer to your question.