I did my update through the LG download and have very inconsistent wifi calling. Also lately when I leave wifi to get back on the network it won't connect to the 4glte. I have to turn on airplane mode and turn it back off to get it back on.
I actually have this case for the S4 and I love it. I have dropped my phone with it on on several occasions and does a great job of protecting your phone.
I don't post much, or ever, on here, but as a possible G3 owner thought this link might be helpful to current owners. I scanned the thread titles and didn't see this anywhere yet.
LG G3 - 40 Tips & Tricks for LG's most powerful smartphone ever