Jumps/drops in heart rate measurement.

Hello everyone,
I've been noticing some strange "jumps" and "drops" in my heart rate tracking lately.
As you can see although the pace is constant there are points where in a few seconds the heart rate reading spikes and falls varying by even 20bpm in a few moments.
Is this normal? Is there any way to adjust this or should I be concerned?

Thank you in advance for your help.