How did you patch the boot image with 24312 if you couldn't get it to boot. I haven't been able to do that.Same as you, I got into bootloops. But then I flash the A13B2 factory image without wipe to make it booting normally, then I flash the boot.img which patched with 24312 to retain the root. Tried rebooting a few time afterwards, now it seems running fine. No idea why it got into boot loops when it was updated from 24310 to 24312 in the first reboot.