Yes it appears like you are correct. It is APN problem, specifically changing the APN from IPV4/IPV6 to IPV4 fixes this issue for me. it seems like the rom doesnt work correctly with ipv6 on this device. This is what i had to do to get it working.
Download app 4G LTE Switcher app from google play.
Install and open the app.
Pick the 3rd option that says “Hidden Settings”
Now in search box in Hidden Settings search for APN.
Click on first option called APNs - Settings APN Settings
You will be taken to apn settings screen of device. It will say “Access Point Name settings are not available for this user”
Disregard that and click on the + on the top right hand of the screen.
Add the following apn:
APN name : Verizon 2
APN: vzwinternet
MMSC: http://mms.vtext.com/servlets/mms
MMS port: 80
MCC: 311
MNC: 480
Apn protocol: iPv4
Apn roaming protocol: iPv4
APN type: default,supl
Hit the 3 dots at the top right corner and hit SAVE. it will appear as if nothing happended or this didnt work.
Go back into the APN menu and you will see your new APN you created. Click the circle to set Verizon 2 APN you just created and your phone should start picking up data. if it doesnt just turn airplane mode off/on or reboot phone and you should be good to go.
Please keep in mind that the device still will not work for making calls because that is run thru VOLTE by verizon. This rom does not support VOLTE on this device. So for calls you will need an app that runs over the internet, a VOIP app, but this fix alllows you to fix mobile data issue on this device. Hope this helps someone. The phone runs really well not. 100mbs down in some areas!