I know nothing about Google Fi, but some quick googling leads me to understand you're using a normal Android phone, and you're roaming on one of the local mobile networks here. Plus, with Google Fi, your phone will try to connect via WiFi when it can. Do you have a local SIM card?
Do you see H or H+ icons in your phone display? Or are you intuiting the technology from the speed of your connection?
Does your mobile phone support LTE band 28 (700MHz)? This is the band used for in-building coverage here, since low bands propagate better than high bands through bricks and concrete. If your phone doesn't support B28, in deep indoor coverage it might well get service on 3G (H/H+) in bands 5 (850MHz) or 1 (900MHz). Once you're out and about, your phone will have no problem getting service on band 4 or 7 (high bands).