Current pace issues - Fenix 6 pro

I've recently purchased a fenix 6 pro as an upgrade from my FR654M and been really disappointed with the accuracy of the current pace data field. It seems to always read a lot slower than the actual pace and a lot of runs actually come in slightly short distance wise. The pace on the FR645M has always been pretty much spot on. Comparing the pace plots on connect between the 2 watches the fenix is very up and down with a lot of peaks and dips, whereas the 645 is quite linear as it should be. Is this a common issue with the watch or should I return it for a replacement?