Have you tried rebooting your phone by holding the up and down sound buttons, this should then do some kind of system check (I think), I have a Z30 and was having some problems and did this (it should work on all BB10 devices) and it seems to have resolved it.
When I first got my Z10 a few months ago it was doing the same thing. Thought it was defective but before I returned it I wondered if perhaps something was loose. Opened the back and it looked like the SIM Card wasn't quite seated. Also played with media card and battery to ensure they were in solid. That fixed it.
The OP says it only started after updating OTA to 10.2.1.1925. That's why I was suggesting the problem is software based, and to use an autoloader for a clean install.