It looks like Pangu has pushed a update in their app to fix a few issues with the jailbreak. Like the Cydia Substrate loading issue upon reboot, iMessage, and Safari bugs. This update should be done ASAP.
To apply this update just go into the Pangu app on your device. Now click manager then you should see the update. Now just tap the download arrow and it should install. It would be best to not have Touch ID or a Passcode set when you apply this update just to be safe.