assuming you've used the TLA for heart rate varriablity.
high variability is good,
if your heart makes bigger changes in speed faster, it means you're healthier. Think about your heart slowing down after a run.
I think it also only gets a value if your heart rate is changing, so if you're heart rate is fairly steady, then it won't have a number.
If you only have a number when you do breathe, your heart rate is sitting high, and must drop when you breathe.
or maybe you're doing breathe early in the morning, and just haven't been active enough to get your heart rate up yet.
*TLA - three letter acronym - handy but sometimes confusing in forums where a lot of topics are discussed. Helpful for others to get you the correct help if you spell it out at least once in your post