When Luca released the Yalu jailbreak for iOS 10.1.1, a lot of users were complaining that Cydia crashes constantly. This wasn’t surprising because the jailbreak was intended for developers rather than normal users. However, someone from the community created a stashing package called YUCCA Utilities to fix this issue.
YUCCA Utilities stashes your system to fix the Cydia crash issue as well as low-storage warnings. A while after this package was released, Luca warned several times that jailbreak users should avoid installing this package as it does more harm than good. Unfortunately, users still continued to install it and some even started facing issues.
Now Saurik, the man behind Cydia, has also posted a warning that users should avoid installing this package. He states that the package is ‘so broken’ that his only recommendation for those who installed it would be to restore their devices to iOS 10.2 to fix the problems that it creates.
I am concerned the YUCCA package is so broken the only real recommendation I have is to restore your device to 10.2 (though I’d also recommend waiting until Luca releases a jailbreak and just hope that when that happens iOS 10.2 is still a restorable option).
As for Substrate, I wouldn’t worry too much about anything: I’m pretty certain your “worst case scenario” is to hold down volume up while running a new mach_portal, which will disable Substrate entirely, at which point you can fix any issues you have via Cydia.
Luca also warned against the use of any kind of Cydia Substrate enabler, however Saurik states that it is not a big issue as you can simply boot into No Substrate Mode if any package is causing issues and then remove it via Cydia.
Therefore, if you haven’t installed YUCCA Utilities yet, then stay away from it. But if you did install it, then Saurik’s recommendation is that you wait until Luca releases the iOS 10.2 jailbreak and then restore to that version and re-jailbreak. For those who are on iOS 10.1 or iOS 10.1.1 and haven’t jailbroken yet, I’d recommend that you also wait for the iOS 10.2 jailbreak.