Heart rate showing gaps

Hi there

I have an Apple SE watch and when I look at the health app,

it is showing gaps in my heart rate. I had my watch on the entire day yesterday, and it is will not showing a solid bar on some hour periods, however, if on others it will show the bar.

the main reason for me swapping from my Garmin to this watch (which I LOVE!) is that I can have certain epilepsy detection apps that allow my wife to be notified if I have a seizure. I also need to track my heart rate for my seizure detection as I have nocturnal epilepsy and sometimes heart rate is how I detect any seizures, or even any seizures I might get during the day.

why does this happen?

Thanks;

ashie