What I did and it works like a charm:
Step 1. Hard Reset Watch 3 (Hold down crown button and power button until screen goes black. When apple logo comes on take your finger off crown button and hold power button until you see the watch prompting to erase all data) Erase all Data
Step 2. Delete watch app on iPhone and then download it again on iPhone.
Step 3. Bring phone and watch closer to wifi modem.
Step 4. Put watch on charger
Step 5. Put Your phone on airplane mode but have Bluetooth and WiFi turned on.
Your good to go then.