Why can't I get mobile data? (Verizon LG G5, China Mobile SIM)

I just got an LG G5 with Verizon last month, after my G2 started getting too slow and sluggish. Both times, the retailers told me the phones were already unlocked for international use. When traveling in China (PRC) the G2 was able to get mobile data (albeit not always reliably) with my China Mobile SIM card. Now that I am back in China with my new G5, mobile data no longer works with this same SIM. I can still make/receive calls and SMS text messages with my Chinese phone number, and can connect to Wi-Fi networks, but mobile data is unable to connect.

The SIM card was cut from Micro to Nano size with an Aerb card cutter, and at first I was worried maybe there was damage, but I inserted another purely nano-SIM with a different China Mobile account, and was still unable to connect.

When accessing the phone on the "Enter PIN to unlock" screen, the upper left corner indicates the "CMCC" network is supposedly connected:

http://i.imgur.com/Tnj0M7P.jpg

Also shows up every time I pull down notifications:

http://i.imgur.com/GgL52sD.png

The notification that the "SIM card is not from Verizon" doesn't do anything when clicking on it, and is swipeable/dismissable. Doing so removes the SIM card notification icon with the question mark inside it on the upper left of the screen. (See following screenshot.) This used to show up on the right hand side on my G2 and was never dismissable.

http://i.imgur.com/7pjzP14.jpg

But I still can't access any internet. I get the above message in Chinese soon after almost every reboot: 网络连接有问题，请检查后重试 ("There is a problem connecting to the network, please check and try again").

(RE: other notification icons: the "E" next to the signal bars is what always showed up before in China on my G2 as well, instead of "4GLTE" as when back in the US on Verizon, but used to have up and down arrows underneath it indicating traffic. These arrows are completely absent now.)

Under Settings -> More -> Mobile Networks, I've tried to enable roaming data "access for all trips" and "only this this trip":

http://i.imgur.com/FmVZlUm.png

http://i.imgur.com/o4oBqq7.png

http://i.imgur.com/Pk2Otus.png

Under Settings -> Mobile Networks -> System Select, the Network Mode is set to "Global" by default and the second setting is greyed out:

http://i.imgur.com/PpJGrU7.png

Since China Mobile is GSM, I also gave a try at actually specifying the network mode to LTE/GSM/UMTS:

http://i.imgur.com/uof46th.png

This un-greys the second setting to "Select network submode and network operators":

http://i.imgur.com/aTY9xsn.png

Initially, the Network submode says LTE/3GPP multi. I try and click the second setting to "Select a network operator":

http://imgur.com/9wAmABi

I choose to "Search networks"...

http://i.imgur.com/7iVmhtt.png

The result:

http://i.imgur.com/Oy9ZVUj.png

I choose CMCC, and get returned to a previous page with the message, "Registered on network" at the bottom of the screen:

http://i.imgur.com/ZHT6Jle.png

Still no internet connectivity.

I also try to specify the network submode to "GSM/GPRS/EDGE only"

http://i.imgur.com/eam6V7J.png

When searching "for all available networks", this time only the GSM networks show up, and I choose CMCC again.

http://i.imgur.com/5HFj6Zn.png

Still no luck.

"Network type and strength" keeps showing me "2G". This has been the case with every permutation of settings I've tried so far:

http://i.imgur.com/JH8QL87.png

Going to Settings -> About phone -> Network...

http://i.imgur.com/iKS2luW.png

These are my statuses no matter what I try so far. "Mobile network state" is always "Disconnected" and IP Addess is always "Unavailable":

http://i.imgur.com/t67mCRF.png

Went to a China Mobile service desk, and they could offer no help other than to try another functional SIM card to seemingly confirm that only my phone in particular can't connect to a mobile data network.

Is my phone simply just locked? If so, how do I unlock it? Or is there some other problem?