More than likely, you've got some tweak installed that is incompatible with the iPad or your iOS (or both). IMO, that's why Mobile Substrate keeps throwing you into Safe Mode.
So, I think you've got a Mobile Substrate-using tweak that is not working properly. If you can remember, try to uninstall any tweaks you loaded just before this behavior began. Or, if you have SBSettings installed, turn off all the Mobile Substrate items. Then, turn them on, one by one (respringing in between) to see if you can find which one is the culprit. If you locate one that is causing the issue, then uninstall it from Cydia (but make sure it's turned ON in SBSettings - else it'll cause additional issues).
If you can't remember what tweaks you've installed or the checking Mobile Substrate items doesn't help (or you don't have SBSettings), may I ask that you list all the tweaks you currently have installed. Maybe we can help you ID the "culprit(s)"...
Marilyn