Fenix 5s GPS never ceases to amaze

Nothing to do with your watch, its the sketchy satellite coverage in your part of the Globe...

You might want to try different GPS settings. Gps, gps + glonass or gps + galileo. Depending on the area where you are they can give different results. You can find this in the run settings of your watch. Buying a new watch (Garmin or Apple) is not likely to fix your problem. Try a few runs with each setting and if the problem is still there, contact Garmin again. 

surely you jest, Singapore having sketchy gps coverage?  One of the worlds busiest areas of skies and water ways all totally reliant on gps.

I've never had much luck with the GPS in cities. Tried it in central London, Paris, New York, Boston, etc, etc. Some bits are 'fine' the rest is like a five year old trying to draw between the lines. In NYC I ended up in the Hudson after showing me zig zagging across 20 blocks. That was a 20 block straight walk to the hotel. I have often thought if I lived in those locations, I wouldn't have bothered buying a GPS watch.

I've noticed this just recently with Fenix watches.

I did the Moscow half marathon on Sunday and at one point my GPS track goes doolally (whether GPS, GLONASS OR GALILIEO). This has happened in previous races around the same area with different GPS settings.

I had a look through other peoples tracks and found that those with Forerunner watches had perfect or almost tracks while the Fenix users all had the same glitch at the same location.

Look at the middle section of my track and you can see my problem: https://connect.garmin.com/modern/activity/3962194639

Forerunner tracks:

https://connect.garmin.com/modern/activity/3962066644

https://connect.garmin.com/modern/activity/3962128444

https://connect.garmin.com/modern/activity/3962141385

https://connect.garmin.com/modern/activity/3962146938

Fenix tracks:

https://connect.garmin.com/modern/activity/3962302484

https://connect.garmin.com/modern/activity/3962118058

Why why why?????

I wonder the same thing. Would a stryd pod be better or would I miss the watch factor ie interface on the go.

I have a stryd pod. My GPS track itself still comes from the watch as stryd has no GPS. But distance pace from stryd has been great. No worries about drops outs from sketchy satellite connection caused by tall buildings or heavy tree cover. 

I "upgraded" from a fenix 3 to a fenix 5 and I can tell there's objective and definite decline in GPS performance. My girlfriend still uses the 3, so we've had quite a few parallel maps to compare. It's night and day difference, worst investment I've ever done.

Even it's own previous version did way better.

You can also refer to this article https://fellrnr.com/wiki/GPS_Accuracy

There's a ton of data in there. E.g. "GPS plus GLONASS produces less accuracy than GPS alone"