After a long time “ignoring” iOS 12.1.1 beta 3 so users can freely return to this version to jailbreak. Today, Apple has officially un-signed it.
This information is confirmed by the author of unc0ver – Pwn20wnd. HIs twitter stream with the message that Apple officially signed the sign of iOS 12.1.1 beta 3. See as from this point, if you are in iOS 12.1.3 or above, you cannot return to the old version to jailbreak, unless you have saved SHSH2 blobs to return to the un-signed version.
Currently, iOS 12.1.3 is not completely jailbroken. Recent exploit codes like voucher_swap, v1ntex, v3ntex, and machswap are only compatible with iOS from iOS 11.0-12.1.2.
If you are using iOS 12.0-12.1.2, you should keep your version the same if you want to maintain the jailbreak for the device.
If you’ve “in” iOS 12.1.3 but are still interested in jailbreak, it’s best to “stay” there because in principle you should be at the lowest possible version to have the opportunity to jailbreak the device.