How's pace/distance compared to other watches/phone?

I currently have a Fenix 6s pro solar. Pace was never really good compared to my phone and the distance often a bit too short on measured tracks. Since a recent firmware update my pace tends to be about 0:30min/km slower and the distance shorter by quite a bit. Some clever guys in the Fenix forums have tracked it down to potentially GPS shutting down and the accelerometer taking over when GPS signal is just a bit weaker. I see this the following way: A tree is near a road. I get closer and pace goes down. I run past the tree and pace still goes down. Way past the tree pace might actually go up again. While running at fairly constant pace. With regards to distance the first km might just be 10m short, then the next one an additional 30m, then another one an additional 20m, then one 90m short, etc Doing intervals is completely useless as the watch might not react to me running faster. And with the Garmin coach programme I'm currently doing I need to run substantially faster to get towards my goal pace on the watch. While I'm running faster than goal pace on my phone. Thus useless.

Question after this block of text: has anyone tested this? How well does the 945LTE get the distance of measured tracks and get the proper pace even when there's a tree or a building nearby?