I called Garmin UK tech support today to see if they are aware of any GPS issues. I explained that I had a F5X that I really liked but decided not to keep due to it performing much worse than my FR935.
As expected, the tech rep said that they are not aware of any GPS problems with the Fenix 5 series and that they have not seen any evidence to the contrary.
On being asked whether they ever look at their own forums for evidence, I got told that they had not been made aware of any problems by the community managers as of yet.
I understand that Garmin wouldn't admit to an issue existing with their flagship line of watches at this stage but it seems that the company is, yet again, blissfully unaware of any issues surrounding the Fenix 5 series...