Reconnection issues

I have experienced the same issues occasionally. No need to power cycle the phone, just toggle bluetooth using the control centre.

What peter_ska said... if that doesn't work (it usually does), force close the app and start it up again.

I have the same problem frequently . For instance, if one of my kids comes to play with me and gives me a Hug the watch disconnects itself, and then (sometimes) reconnects again. Sometimes it looks lije it is connected, even I get the WhatsApp notifications in the watch but the I unlock my iPhone and go to GarminConnect it cannot "see" the watch . In those cases toggling bluetooth on and off gets it solved.

We know that iOS 11 introduced some Bluetooth issues that affect how Garmin products connect with Apple devices. While we have taken efforts to rectify the problems being reported, it has been determined that these are issues that Apple needs to address. We apologize for the inconvenience, but for the time being, your Apple device will need to be power cycled since the phone is responsible for connecting to the Garmin device. If the phone does not try to connect to the device, there is nothing the Garmin device can do to force it to connect.

Reports have also been circulating that the latest beta of iOS (11.1) does address some connectivity issues, so it appears that Apple is continuing to work on it.

Garmin Outdoor SW Quality Team

In my case I would say the issue is more complex than that, In the Bluetooth settings of the phone the Fenix 5 is reported as connected but Garmin Connect doesn't recognized it. If I turn Bluetooth off and on again on the phone, it connects back to Garmin Connect...
only saw this issue appearing in the Beta 6.71 version.
I don't think Apple is responsible since other Bluetooth devices seem to connect correctly and the phone recognizes and connect to the Fenix, Garmin Connect NOT.

I upgraded to the latest IOS 11.1 beta2 yesterday and since then Bluetooth between iphone and Fenix 5 has been better. Was getting disconnected frequently. I thought this had fixed it but its just disconnected one again (24 hours since update to beta IOS). Need to toggle Bluetooth on the phone to reconnect. I'm not sure if this is an Apple issue or a Garmin issue. Also running 6.71 on fenix 5.

In line with what odsweng has already posted in this thread, my experience of this issue is that it?s absolutely a problem at the iPhone end. No amount of BLE on/off cycles, power on/off cycles or ?soft? resets on the Fenix 5 will clear the issue, but a simple toggle of the Bluetooth on the iPhone (a few seconds pause with Bluetooth Off is usually required) seems to clear the issue. Thus my deduction that this is a problem at the phone end and not the watch.