Hey there,What boot.img are you refering to?
I tried flashing vendor boot (fastboot flash vendor_boot .\sake_vendor_boot.img) like stated here and than booting into twrp (fastboot boot .\twrp.img) like stated here. But after reboot it stucks at ASUS logo, till I hardrestartet it. Happens everytime. booting to TWRP without flashing vendor results in the same outcome.
Btw. I had the same outcome even bevor flashing LOS recovery and LOS.
so you havn't seen TWRP at all, right? Didn't boot, stuck immediatly?