I assumed you got "continuous" monitor set on the watch. By default it's set at "every 10 minutes while still". So far I have no problem... I don't think GPS is the factor.
Unfortunately this watch is a disaster when it comes to the accuracy of the health sensors compared to the competition.
I say this as someone who bought both a classic and standard model at launch.
Samsung should be embarrassed putting out a product so buggy, when the competition at both the premium and budget end do better. Reviewers of the watch looking at it from a health and exercise tracking perspective are slamming it all over social media, bit of a PR disaster, I wonder if Samsung cares.
I had vowed to abandon Samsung's watch line after the poor performance or the active 2 and the void that was Tizen, but Samsung shocked me and rejoined Google in WearOs. Surely their new tracking sensors were the answer to their spotty tracking as well!? NOPE, same old Samsung. 3 consecutive watches with terrible tracking and I'm not getting burned again. GW4 will be returned