Here is the procedure I tried:
Unlocked the bootloader
Did a full restore to MHC19I through fastboot
Flashed this boot.img
( This is so I can encrypt the user data partition after getting into Android, and it also allows a system-root without getting a boot loop )
Flashed the twrp-3.0.0-1-angler.img recovery
Locked the bootloader
Booted into TWRP without ever going into Android yet
Sideloaded BETA-SuperSU-v2.68-20160228150503.zip
Booted into Android and setup with my Google account, I used a fingerprint and set a PIN, and selected "PIN required on startup"
Update all the stock apps, with some reboots in between
Then encrypted the phone through security settings
Now here is where I’m having trouble.
When I boot into TWRP after having encrypted the user data partition, it asks for my password, as it should, but it won’t take my PIN. It tells me "Password failed, please try again" and "Failed to decrypt data." Is the password prompt not asking for the PIN I set? Does TWRP only support decryption with a password, or something? Can I not use a fingerprint to lock the device? What am I missing here?
Is there perhaps another procedure to getting Android setup with TWRP, root, and user data encryption while ending with a locked bootloader?
Thank you in advance for all your help!