Here are your options. Check with your ISP and see if they provide ipv6. If so, have them check the cable modem and make sure its enabled. Then make sure your router also has it enabled. To fix the WiFi bug, your phone must be provided an ipv6 address. If ipv6 is enabled, but you still don't get an address, you can change yo router to tunnel ipv6 into ipv4. And you won't have the WiFi sync bug. You can check your ipv6 settings by going here test-ipv6.com.
If the first option doesnt work you can do this. If you have a google voice number, your can use Hangouts to make VOIP calls. Download Hangouts Dialer from the play store. Go into options and set hangouts to answer calls. Goto the LG dialer and dial *72???-???-????, the question marks being your Google Voice number. That will send all calls to your google voice number and make hangouts ring on calls to either number. Then when you want to use WiFi, turn on WiFi, and airplane mode. When you want to use cellular data, turn off WiFi, and airplane mode. As long as WiFi and cell are not on at the same time, you will not have the WiFi sync bug. And you can still make/receive calls using VOIP and Hangouts.
Your third option is to leave WiFi off all the time, and make Verizon credit you for any data overages this problem causes you. It is their fault anyway that you are having this problem. Hope this helps. CV