Apple has made watchOS 4.0.1 available to the Apple Watch Series 3.
According to the release notes, the minor update targets a bug that prevented Watch Series 3 wearables from properly connecting to WiFi networks, which in turn prevented LTE connectivity.
“watchOS 4.0.1 fixes issues that, in rare cases, were causing Apple Watch to join unauthenticated (captive) WiFi networks, such as those found in public places like coffee shops and hotels, which direct the user to a webpage before the network can be accessed,” explained Apple.
The update should resolve the issue. WatchOS 4.0.1 is free to download over the air.