No cellular network after OTA to lollipop (Nexus 4)

I have a Nexus 4 with Kitkat, working fine with t-mobile (USA). Yesterday, I did an OTA to Lollipop. But after that the cellular network only briefly works.

First problem, I encountered was the lack of data connection, but after I changed the APN setting, it worked...but only briefly. Every time I reboot the phone, it can make phone calls, and access the data network for a few minutes (or sometimes I have no access to begin with). But then the network indicator becomes either an 'empty triangle' or a 'full triangle with an exclamation point'. Then, I can't make phone calls or use the data afterwards.

Very strangely, I just found out that if I connect to wifi, I can make phone calls suddenly. If I turn off wifi, I can't make phone calls any more. What is going on?

Does anybody have the same problem? Does anybody a known workaround?

My current APN setting is:

T-Mobile GPRS

APN: fast.t-mobile.come
Proxy: not set
Port: not set
Username: not set
Password: not set
Server: not set
MMSC: http://mms.msg.eng.t-mobile.com/mms
MMS proxy: not set
MMS port: not set
MMC: 310
MNC: 260
Authentication type: not set
APN type: default,supl,mms,dun
APN protocol: IPv4
APN roaming protocol: IPv4
Bearer: unspecified
MVNO type: none
MVNO value: not set

Further testing using '##4636##'

• GSM service: in service


• GPRS service: disconnected


• Network type: UMTS


• Call redirect: false


• Call status: idle


• radio resets: 0


• data attempts : 0


• 
  

  data successes: 0

  
  


• 
  

  cellinfolistrate 2147483647

  
  


• IMS registration required is 'off'


• SMS over IMS is 'off'


• SMSC: _______ [update][refresh]


• Toggle DNS check: 0.0.0.0 not allowed