Especially on small circles like 200m track. Look on the image! Actually, it is the worst image I ever seen on Strava! Compare my new 5 plus (on the top) and iPhone (bottom). Even cheapest Android costs 10x less than Fenix has much better GPS performance. Even my old Vivocative HR had MUCH better tracks. Now I shame to publish my runs from my 700 euro device, they look just terrible. I can't understand how Garmin was able to make a product with SO bad performance of its MAJOR feature.
до покупки F5+ пользовался 735,проблем с GPS не испытывал, решил взять F5+ и пожалел, через раз получал трек (вид занятия бег) как на картинке обведённой жёлтым, дико бесило, но нашёл причину плохих треков…
The reason why I publish this is my hope that eventually Garmin will hear us and finally will improve GPS performance. I have read that Polar made great FW GPS-related improvements so now they works nearly…
Are you in Russia? What latitude are you at? Have you tried GPS + Glonass instead of GPS + Galileo?
I ask because Glonass is supposed to have an advantage at high latitudes because the satellite orbits…
Could you please record the activity at the SAME location, so the same athletic track run, at the same time, recorded both with your iPhone and your Fenix. Fenix is extremely bad, and "drunken" at walking paces, but when you run, with the higher speed, and the unit being horizontal a part od the arm stroke, the track should not be that bad. New Sony chipset on 2019 devices should technically be even worse. Please note that the satellites move, so if you measure at different times, that might be the source of errors, iPhone having a favorable overhead situation, and Fenix not. Not an exact science GPS signal is 
I run this track almost every day and I can prove that even though there are some "better" and "worse" days, overall all devices yield very similar results. Look at the Vivoactive HR and Xiaomi Mi6 tracks, four years old not-premium devices (Mi6 image is from NRC that does not sync to the Strava), all images are from exactly same track. In fact, it seems that Fenix 5 Plus has WORST GPS on the market. I wondered tracks from the recent Parkrun, noticing devices name that guys wore and Fenix 5+ is DEFINITELY worst. You said that iPhone having favorable overhead situation but in fact $50 Amazfit has the same but performs MUCH better. I drastically disappointed by my new device. I basically like all other Fenix features and overall impression BUT GPS! Sounds like Stryd is not fancy devices anymore but dire necessity because I simply can't believe F5+ reported results. Good to note that even though Vivoactive HR drew more-less nice plots, it constantly understated my running pace on 30 sec/km on average, that is a lot! I liked to think that is the way how Garmin prepares athletes to competition :) But with F5+ I guess there is no accuracy at all. Note GPS + Galilieo track. It is _a bit_ better but still very bad.
Okay, here is direct comparison of the same run I did yesterday. Except of 2-3 laps registered by Xiaomi out of the track, that probably led to some distance overestimate, I believe that results much more precise also because of these results proven by stopwatch/distance method. Note that my smartphone was in belt poach so was in worse reception conditions compare to watch. F5+ underestimated 10k by 700m! That is 7%. I think it is horrible.
Yes, F5+ works no so bad on the straights so I don't think that I have to contact Garmin but these circle tracks is just nightmare. 
