iOS 8.3 is no longer signed by the Apple company for installation in iPhone, iPad and iPod Touch, so the downgrade from iOS 8.4 it became impossible from tonight, so if you are not happy with this version of the operating system, you have no choice but to keep it.
Apple launched iOS 8.4 a week ago and it was normal to close the signing of SHSHs for installing iOS 8.3, as it does every time it releases a new update, the action being taken just a few minutes ago.
Considering that there is 8.4 iOS jailbreak at the moment, there are no reasons to leave iOS 8.4, because the performance of the operating system is not so bad to motivate the return to an older version of the operating system.
The Apple company acts in this way every time it releases updates for iOS, although it generally closes the SHSH signing "windows" much earlier for the old versions of the operating systems for its iDevices.
In this situation, stopping the signing of SHSHs has no effect on users, and that's because we have jailbreak solutions for all iOS 8 versions released so far, and you can find tutorials for each one in the jailbreak and decoding table.
