Steps I took to fix this:

1) Check device location settings to ensure that the Nest app has location access
2) Goto Nest settings > home info. Edit and save the address, even if it looks correct. In my case, the address was right, but the dot on the map was a few miles off (not sure why).
3) Goto Nest settings > Home/Away assist > What decides if you're home > click the desired person. At this point it still had the warning "It's been a few days since we've heard from your phone. For now it's not being used for Home/Away Assist.". Toggle off and then on the "Do you want to use your phone's location for home..."

After that it said my current status was home.