Accuracy of Apple Watch series 8

Has anyone else discovered errors in the monitoring of aFib and the Apple watch seemingly inaccurate readings?

I have an Apple Watch series 8 and use it among other things to provide feedback on health issues. For the last 3 months the data has been showing that it estimates I am in aFib 35% of the time or more, which is unusual for me.

After visiting my cardiologist and going through a 2 week monitoring by a medical grade device, there was no similar readings, while my watch continued its estimates.