Well, I don't really know. I initially did what I always do: extract the new boot.img from the update, patch it with MM, run flash-all without -w, let the update finish, reboot and flash the patched boot to boot_a and boot_b. That bootlooped. I flashed stock boot.img and ran like that for a day. Next I booted (but didn't install) TWRP, and tried to install 19.1 (bootloop), and 18.1 (wouldn't install). I decided to try to downgrade to the April update and did flash-all from there (without -w). Big mistake, because then it stuck on the G screen and wouldn't boot at all. I ultimately was able to flash back to the May update, get it to boot, then followed your directions. I did have to install 18.1 first, because even after following your directions, 19.1 still bootlooped when installed from TWRP. MM was able to update to it fine, though, from 18.1. Who knows what the problem really was.