I reviewed many of the comments in this forum regarding connection issues with the Garmin Index Scale (GIS). Hopefully, this troubleshooting guide will help the next person having connection issues:
To set up the GIS initially using your phone:
1. Ensure that the communication protocol settings for your router or the network you are connecting to are set to 802.11 b/g/n or 802.11 g/n with WPA2 AES encryption (https://www.howtogeek.com/204697/wi-fi-security-should-you-use-wpa2-aes-wpa2-tkip-or-both/ ) at a frequency of 2.4Ghz. The GIS does not use the more current encryption protocols and does not support the 5Ghz frequency.
2. You can set the DNS servers statically in your router for Google https://developers.google.com/speed/public-dns/docs/using (primary: 8.8.8.8 secondary: 8.8.4.4), but I prefer Quad9 https://quad9.net/doh-quad9-dns-servers/ (primary: 9.9.9.9. secondary:149.112.112.112) for privacy and security. Both public DNS services work with the GIS.
3. Ensure that, when using your phone to set the GIS up, that the Garmin Connect App (GCA) is installed and Bluetooth on your phone is turned on in order to pair the scale with your phone during the initial setup process.
To reestablish network connectivity using your phone:
1a. Follow Steps 1 through 2 above.
2a. Select the .../More in the bottom right-hand corner on the main page of the GCA.
3a. Scroll down the items list and select "Garmin Devices".
Note: You should see the GIS listed as a device, if not you will need to select the "Add Device" menu bar at the bottom of the screen to walk through the pairing process again before proceeding to the next step of connecting to your network.
4a. Select the GIS.
5a. Select "Device Settings".
6a. Select "Wi-Fi Networks".
7a. Press button on the bottom of your scale for at least 5 seconds or until the screen clears and the "Spanner of Death" appears along with the wireless icon in the upper left-hand corner of the screen on the GIS.
8a. Wait for it...This may that awhile until the GIS scans for your network. Once it finds compatible networks, the Wi-Fi/Bluetooth/ANT icons will flash briefly in the upper left-hand corner of the GIS screen and then only the Bluetooth icon should remain.
9a. The GCA should then present you with a list of compatible networks, assuming that you followed steps 1 and 2 above, select your network from the list that appears. A check mark should appear next to the network name when you select it.
10a. Select the back arrow in the upper left-hand corner of the "Wi-Fi Networks" screen and back out of the GCA to the main screen (Wi-Fi Networks > Settings > Settings > Devices > More > Main Screen).
11a. Assuming that the scale successfully connects to your network, you should see a large "Check" mark appear on the screen of your GIS.
11a. To test that your GIS can successfully transmit data to your Garmin Connect Account (https://connect.garmin.com/) and update the weight widget in the GCA on your phone by performing a weigh-in.
12a. Ensure that when you step on the scale your name or initials appear, from when you added your information during the initial setup, and that you wait until the >>>>>>> progresses across the top of the GIS's screen until it completes with a "Check" mark.
13a. Check your GCA, the weight widget should appear on the main screen (“My Day”) of the GCA with your current weight. If it does not, ensure that you have Weight selected to be "SHOWN ON PROFILE" by navigating from the main screen in to Profile & Privacy (.../More > Settings > Profile & Privacy > SHOWN ON PROFILE).
14a. If all goes according to plan, celebrate! If not, you may need to go into your Garmin Connect Account online and delete the GIS from the list of devices on your account and delete it from the “"Garmin Devices" list in the GCA on your phone, to remove any conflicting data, then walk through the initial pairing process and reentering your personal data in the GCA before returning to “Step 6a.” above.
Cheers!