Cannot recieve calls or SMS after losing network coverage.

After passing somewhere where I lose network coverage, I cannot receive any calls or SMS, even after the phone is reporting that network is now available again.
This does not happen every time, so I cannot describe steps to reproduce, but maybe I can post some log that will help me narrow it down.
The only way to receive calls or SMS again is to either reboot the phone or try to make a call. When I do this, the call takes quite a while to start (I have to wait about 20-30sec before I hear the calling signal).
Like I said, this does not happen every time I lose network coverage, but still happens quite frequently, and it is *really* annoying when it does as I become pretty much in-contactable while this lasts, even though the phone displays network signal.
I hope I was clear, but please request any more information if required.

Phone: BQ Aquaris E4.5
OS Version: 15.04 (r23) [Although the issue was present on previous versions as well]
Network provider: Uzo (uses MEO network)