Been having issues with Nexus 5 now for a while and don't seem to be able to resolve it, originally my partner had the Nexus 5 from new since December 2013. She complained like hell about it so eventually I got in contact with Google and got them to agree to a new replacement device (I then kept the new one and she had my S4)
At numerous points through out the day the Nexus 5 while go into "roaming mode" (H+/4G logo replaced with R at the top) and the only way to get it out of Roaming mode is to go into Settings>More>Mobile Networks>Network Operators, from here to manually scan and then select auto again.
Google Play have sent me 3 replacement devices incase of a hardware issue but all 4 phones have had this issue now, my partners S4 and S5 dont suffer with the same issue and she is on Three aswell.
The one thing I have noticed is when I manually scan for networks Three comes up twice in the list, so maybe its an issue auto switching between then two?
Google keep trying to get me to run in safe mode, do factory resets etc but nothing works, I have now sent them a response today basically saying I've had enough and want to return the item so I can go out and buy a HTC One M8 (not holding my breath)
Nexus 5, Android 4.4.4 KTU84P on Three UK.
Anybody else had this? it seems to be Hardware and Network specific