I've driven areas with no map tiles before, when cellular data was both strong and weak so it could be either weak connectivity or a problem on Waze's end. The biggest missing chunk of data I had was about 40 miles long on a road trip. I checked my signal and even pulled up data from other apps no problem, but Waze was dead. In that case, I did a support ticket and they said there was a server problem that day. But in other instances I think it's due to having poor signal / no signal or being on GPRS/EDGE or 1x/RTT low speed data access. Waze is incredibly intolerant of slow data speeds, to the point that sometimes it says I have no connection even in 3G areas and while other background apps work fine.
The two areas where "missing road" URs are filed the most are two different stretches of interstate where only Verizon and AT&T have 3G service… everyone else is GPRS or 1x and I suspect Waze is just being a baby and timing out on those slow connections.
AM for Baldwin
-Mobile Cos., AL // Grenada-LeFlore-Carroll Cos., MS // Escambia-Santa Rosa Cos., FL // CM for the USAMoto Droid Turbo (Android 5.1) on Verizon Wireless