Why are some of the heart rate bars missing?
Note: gaps in Cardiogram data are normal and and do not indicate any health issues on their own. Cardiogram reads data from your wearable, so when data doesn't show up and there's a gap in the data, it's either because no data was collected by the wearable's sensor, or the manufacturer's algorithm determined that the beats-per-minute reading may be inaccurate.
This can happen during workouts, since the watch can move and lose direct contact with skin (e.g. due to sweat). To help prevent this, make sure the watch is in contact with your skin (e.g. tighten the band before a workout).
Cardiogram does not limit the number of data points collected per day. In continuous recording mode, a data point is collected every 5 seconds, and in regular mode it is collected every 5 minutes.