My Apple Watch series 6 shows very high Heart Rate while running

Hi, I am a serious runner. I normally run long distances like 15-20k. I recently upgraded from my old Apple watch series zero to series 6. But sadly, this new watch is showing alarmingly higher heart rates for me. Sometimes it shows a heart rate of about 210 bpm while running. To check the difference, I tried with two other another tracking device from Garmin and Samsung. For the same pace, my heart rate was not crossing HR of 170 bpm at any point. I am surprised to see this difference in bpm. At 210 bpm (as shown by my watch), I might have felt uneasy or fatigued. But no such symptoms were observed during running and thereafter. I want to know from the apple community, how to resolve this issue? Thanks in advance.