In this article I will be explaining what the issue is with the iOS 8 Jailbreak and the reboot-loop which so many people (including myself) has encountered and it is so much annoying because the only way to get out of it is to put your device in DFU mode and restore it with iTunes which is going to cause you to re-jailbreak your device again and download all your Cydia packages again which can be a long mess.
iOS 8 Jailbreak Reboot-loop: Explain and Fix
From all the research that I have done about what is the issue with jailbreak and reboot-loop is related to TouchID and Passcode. There is some sort of bug or hole in the jailbreak that conflicts with the TouchID and Passcode which causes reboot-loop. If you have TouchID and Passcode enabled and you reboot your device, then you are not going to get out of reboot-loop (90 percent of the time) without restoring it with iTunes and your jailbreak will be lost.
This happened to me like two days ago when I installed winterboard. Since winterboard requires reboot and so my device was stuck in reboot-loop. It also caused my device to get pretty hot when I tried to get it boot up but I had no success. Also running your device hot is bad for your battery and it can deteriorate the life of your battery as well.
As I told that TouchID and Passcode is the reason why jail-broken devices can run into a reboot-loop so the fix for it is to disable TouchID and Passcode and you will not run into reboot-loop. You can still use TouchID or Passcode but you will have to remember to turn it off while rebooting or installing packages that require reboot otherwise you will get stuck in the reboot-loop.
One thing that you will notice after rebooting your device (with TouchID and Passcode disabled) is that all your Cydia tweaks are gone and none of your Cydia tweaks are working. This is because Cydia substrate needs to be updated as well. So the trick here is that you just do a re-spring of your device and it will enable Cydia substrate which will enable your Cydia tweaks. The way I do it is use a tweak that has re-spring button in it.
We can not do much right now because the PanGu jailbreak and other tools need to be updated to fix this reboot-loop issue. Once your device enters into reboot-loop, you will have to restore it to make it work again. My advice is to make your sure your TouchID or Passcode is disabled before you reboot your jail-broken device.