I have the G1100 router on one side of my house and have the older network extender hooked up in my garage to help extend the signal. For awhile, I've had them all on the same SSID, but have noticed occassional issues with Chromecasts, Google Home and now more recently casting to a Roku. When changing the SSID on the network extender in the garage, issues seem to have gone away.
With that said, if I wanted both on the same SSID, are there settings in the G1100 that I should change to allow for "hopping seamlessely" b/w networks? I know on the old Actiontec router, I was able to disable IGMP Proxy, etc... but I can't seem to do that on this one.
The G1100 and newer FiOS Network Extenders (FNE) just recently did an update for SON to fix that issue. I'm not sure if the older extenders are a part of that update. It might be better in your case to leave the SSIDs different.