Since update to 19.18 my FR255 has been missing HR during the activities. It happens many times during most of the activities, regardless if I have the HR chest strap or not. Today, after more than 10min of struggling with that, I paused the activity, restarted the watch, resumed - and that helped.
As my trainings are mostly based on HR, that bug makes the device useless.
Shame on Garmin. Again.
Screenshot from today's activity. The restart was about 14min from the beginning.