Does that happen every time you turn the phone off or only when you do it after downloading a tweak in cydia?
Installing tweaks in Cydia was fine because it would only respring, not reboot the phone, after installing them. Until the phone was rebooted or turned off and on again, it would work fine with the tweaks.
I just noticed in the Pangu app it says not to delete a com.apple file and a service related to iOS updates. I had an update blocker in iOS7 and maybe this carried over somehow. In each case, the phone was not manually restarted until after a few Cydia tweaks were installed.
Right now my phone is working fine, and here's the list of what I've done so far:
1) Restored 8.1 IPSW
2) Restored data backup
3) Jailbroke with Pangu 8.0 Mac (no passcode, TouchID or Find my iPhone, Airplane Mode on as per the instructions)
3.5) Enabled Pangu's
JP/KR no Shutter sound option (because I'm in Japan)
4) Turned on iCloud backups (in case it crashes again at work
)
5*) Installed Substrate Safe Mode (I know apps that need this install it but I'm taking things slow right now)
6*) Installed PreferenceLoader (same as safe mode - taking it slowly)
7*) Installed TransparentVolume 8
8*) Installed f.lux
9*) Deleted some prefs files for tweaks I'm not using/haven't installed yet
10*) SwipeSelection Pro
11*) CCControls (beta 1.3 - yes, I realise it's beta and I'm the last person who should be messing with betas!)
I turned the phone off and on again after each step with *. Cydia asked to respring for Safe Mode, PreferenceLoader and TransparentVolume so I powered off and on after respringing.
Also, the official instructions say it's best to do step 3 before step 2 but I forgot! This may be better based on what DigitalDawn said.
Still going strong. Next phase of testing would involve turning passcode back on and then, possibly, TouchID(although I can live without TouchID for now).
CControls is even better than before. So many more options. Wish I could enable/disable f.lux from the CC, though...