I spoke with Garmin Support and I was told the metal case is why the Fenix 5 has such poor accuracy.
I run next to my friends with Garmin watches--usually cheaper ones--and theirs works fine.
I changed the data settings to every second from smart, and hopefully this will keep the most egregious diversions out.
I live in Toronto and I was told to try GPS + GLONASS. I will do this.
The major errors are confined to certain relatively built up areas; however, I'm the only one with a Fenix 5 and the only one with this issue.
The other Garmin users that I run with do not have this problem.
My sense is it's the watch case material (especially in built up areas). This is consistent with what Garmin support said.
I am writing this to warn people away from the Fenix series and metal cases, and to ask for additional suggestions.
I have been given three suggestions:
Data: Every second (Garmin Support)
GPS and GLONASS (a user suggested this)
Let the GPS soak in at the start (Garmin Support) Is this practical ? Why does this matter?
Karim