I have the hangouts extension installed in chrome on windows 7 and windows 8 PCs and a stock Nexus 6 which has hangouts installed as a system app. When I send and receive messages on my PCs my phone doesn't update with those messages sent on the PC. I also have a Nexus 7 on lollipop and it syncs messages just fine. My LG G3 also syncs messages. I have tried wiping cache/data in the app, signing in and out of chrome and the google account on my phone, factory resetting the phone, etc.
Anyone have any ideas? I tend to switch between my phone and PC all the time and would live to be able to have synced conversations.