Apple Admits To Apple Watch LTE Problems Just Before It Ships (theverge.com)
Lauren Goode, reporting for The Verge: Apple's new Series 3 smartwatch starts shipping this Friday, and the biggest feature change between last year's model and this new Watch is that it has built-in cellular capabilities. Except, that cell service isn't entirely reliable. While writing my review of the Apple Watch Series 3 with LTE capabilities, I experienced notable connectivity issues. The new Watch appeared to try to connect to unknown WiFi networks instead of connecting to cellular, when I was out and about without my phone. Within the first couple days of experiencing this, Apple replaced my first review unit with a second one, but that one proved to be problematic, too. Eventually, the company issued an official statement, acknowledging the issue. "We have discovered that when Apple Watch Series 3 joins unauthenticated Wi-Fi networks without connectivity, it may at times prevent the watch from using cellular," an Apple spokesperson said in an emailed statement. "We are investigating a fix for a future software release."
... and they'd buy a turd on a stick if it came with an Apple logo, so you think they care if there's some minor connectivity issue?
I've never once, in 8 years of using iPhones across 6 carriers in multiple countries, ever seen this behavior. You may want to try to reset your network settings or try a factory reset of your iPhone if this is happening to you personally.