My series 4 watch either won't connect or won't stay connected to cellular when away from iPhone.

https://support.apple.com/en-us/HT207578

You may have to erase the watch and start over.

I’ve spent 2 hours in the Apple store and 2 hours at Sprint with the same issue. Sprint even busted out a new watch before throwing their hands up in despair & giving up. Apple & Sprint please work on a solution. I’m about to return an Apple Watch Series 4 for the second time.

Have same issue however with Verizon, I've 3 hours yesterday and 3 hours the day before with both Apple and Verizon with no resolution. Repeatedly erased watch and started over, etc. Went through escalation process with both companies. No joy thus far. Was told by Apple tech that the Apple series 4 watch had to have the phone one to use cellular - defeats the purpose of what the Series 4 stated it could do - With a cellular connection, you can make calls and use data or apps when you don’t have your iPhone. Anyways, getting ready to return the watch as it's no use to me given the current state of things.

There is obviously some technical glitch that needs to be ironed out.

I will try again in a couple of months. I guess I bought a bit too soon.

What was very frustrating for me was the complete lack of transparency about the existence of the problem.

Is it the GPS pr GPS+Cellular model?