Apple Watch giving wrong heart rate readings

Hey everyone,

I own a relatively new (3 month old) Apple Watch series 7 and I've begun to notice that my watch consistently gives out incorrect readings. I will either get:

• Random spikes of 20+ bpm from the correct heart rate back to back (for example, getting a reading of 75, then 113, then 72, then 120, then 121, then 70 again -- when my actual heart rate is in the 70s).
• Momentary readings of what would be considered as tachycardia (100-110+ bpm when resting that last for 5 - 10 minutes) after a period of normal heart rate readings -- when there's no actual tachycardia happening.

I know these readings are incorrect, because as soon as I see them happening I measure my heart rate on my own, and get much lower (and more stable) results.

Before anyone suggests it, I make sure that my Apple Watch is fitted snugly to my wrist, according to Apple's own recommendations, when I notice these things happen. They still do.

I also noticed that this happens more when I'm sitting, for some reason. However, this still happens when I'm also laying down, or standing up.

Does anyone know how to fix this?