I have compared the two ZIPs. In the original no certificates are stored and the installation works. In the rooted file suddenly appear certificates and it does not work. It should then actually work with the deletion of the certificates or?
No, it's the 6315_1.zip itself that needs to be zipsigned.
IIRC, I read that with the new updater, they're no longer allowing the test key being used to do so. It's hard for me to search the 4pda thread though since I don't know Russian and can't translate whatever search terms appropriately.
I could be completely confabulating though...
edit: not crazy after all: https://4pda.to/forum/index.php?showtopic=1000996&st=13360#entry116493465
I also recall some discussion where someone claimed to have been able to downgrade. Again, not finding it right now, and question its validity, since I imagine it would've otherwise made it to the first post, supplanting the no-downgrade warning.
This doesn't help you since you're already on the new bootloader / recovery, but perhaps the other components of a "core" 6315_1.zip could be compatible enough / combined with older versions to preserve the ability to flash testkeysigned updates. For now, I see why everyone is hesitant to flash July+ cores.
That said, based on what Teyes has stated, it looks like the new updater is the first step in eventually supporting OTAs for our devices.
edit: Found this: https://4pda.to/forum/index.php?showtopic=1000996&view=findpost&p=115765392
Maybe it's possible to downgrade to june11, and whereever from there
edit: Hmm, I'm on june27 right now, and was able to root fine.