The problem of the Nexus 5 is caused by a change in the radio/baseband software. It looks like Qualcomm switches off rSAP in new radio versions for whatever reason. Maybe the phone manufacturer has to pay an extra fee for rSAP support? I don't know... I took a look at the baseband software if there is a chance to re-enable the rSAP functions, but I must confess that I don't understand anything that's happening inside.
So far it only helps to flash the 4.2.2 radio software under 4.4.4. See this thread for more info.
The problem so far affects the Moto G, the OnePlus One and probably the Oppo Find 5 & 7. Even worse, a second phone seems to run into problems after a firmware update: the Sony Xperia Z2. Maybe it's also possible to flash the previous radio software separately.
There is one good news: The HTC One m8 seems to receive official rSAP support with the latest firmware update! Let's hope this is not by accident and HTC will also support rSAP in future phones!