I lost some functions of my iPhone 4 with iOS 7 after jailbreak like making phone calls, the camera app, and others too. I don't want to remove the jailbreak.
This problem was happened for me on my iPhone 4 with iOS 7 when there was few free space (less than 1GB) with lots of apps on it. The only solution that helps me was disabling
find my iPhone, full backup with iTunes and manual backup the data of Messages and other apps with iExplorer and PhoneView. And then restore the iOS 7 again and jailbreak.
Because there wont be any iOS updates after 7.1.2 you will not lose the jailbreak opportunity.