Bad GPS in the woods

Normally the F5+ has a quite good GPS-reception in the woods, but any electromagnetic radiation can disturb the reception (power lines, trains, GPS spoofing and jamming). I once had a similar issue with my Fenix 3 after I passed by a guy who started a chain saw in that moment. The reception was disturbed until I stopped the activity and started a new one. It never happened again, so it definitely was not an issue of the watch.

If you follow Garmins recommendations for better GPS-reception and such issues happen regularly in different locations, you should contact Garmin Service. 

Edit:

Have you switched Autostop off? As the current pace has a high error at very low pace, especially under difficult GPS-conditions, I only use it for roadbiking.

A Fenix should have enough memory, so deleting activities does not help (unless you completely filled it with maps and music).

This just happens. If you are wondering why you got any distance and pace at all, it's because it was using the accelerometer in the watch - it falls back to that when the GPS is out, same as when going through a tunnel. It doesn't look like a memory full situation at all since it picked up the satellites later. You can include an activity field for the GPS signal strength if you want to monitor. When you lose it, it also seems to reacquire better when you are standing still but this is not easy to test or confirm. 

Yesterday I went running again, with Gps + Galileo, another strange outlier as you can see.
This was not the worst; after syncing, the wifi no longer works on my Fenix ​​and the Garmin Connect app can no longer make a connection.
Unfortunately I have to make a new topic again, I think about this. I have already tried everything, remove it from the Connect app, he will see the device again but cannot connect it. Help!

(I've got my Garmin since may this year).

For your latest problem, try the bluetooth connection between phone and garmin connect.

Have you tried using just GPS or GPS+Glonass? That is a clear outlier. Of course in theory GPS+Galileo should be better, but it could be worth trying other options as well (for example, here up north in Finland, GPS+Glonass gives a little better results for me than GPS+Galileo).

Also, do you have anything metallic near the watch when you run (which could affect satellite reception)?

Obviously this time the GPS-connection was lost only for a very short time, the rest of the track looks good. Was there something at the point where it was lost (tunnel, power line, a truck passing by....)?

For the other issues, first switch the watch off and on again, maybe also your phone and your router, then try BT and WiFI again. If both connections don't work, delete them and set them up newly.

Thanks to you all! Wifi removed and put back on. Linked via BT (instead of GA) and synchronized in the GA and luckily it works again.

GPS problem: There was no truck or power line nearby. I go for a run on the weekend with GPS only (without galileo or glonass) that worked well with cycling too. I'm curious.

I have now run twice with GPS only and no more strange deviations. Slightly less accurate, sometimes it saves 2-5 meters, so I can live with this.