Here's how to enter Substrate Safe Mode on iOS 10.2 to fix issues after jailbreak on an iPhone, iPad or iPod touch.
Saurik has just released Substrate Safe Mode version 0.9.6000 on Cydia for jailbroken devices. This new version of Substrate Safe Mode not only adds support for iOS 10.0.x-10.2 jailbreak, but also makes jailbroken devices safer to operate than before.