Try creating a new APN entry (settings not listed below are left at "not set"):
Name: T-Mobile
APN: epc.tmobile.com
MMSC: http://mms.msg.eng.t-mobile.com/mms/wapenc
MCC: 310
MNC: 260
APN Protocol: IPv4
APN Roaming Protocol: IPv4
I have a 32GB Nexus 5 and although I shouldn't have to change this, I noted that switching to the "epc" APN solved my problem in certain countries.
Keep us posted!