I've installed AOSP Extended 8.1.0 Oreo on the Axon 7. I'm also using @Chainfire
's Aroma SuperSU Config zip to configure systemless mode. I've set it to sbin mode, with dm-verity disabled, encryption and forced encryption disabled for the data partition, factory reset protection enabled, xbin su binary binding disabled, and SELinux set to permissive. /system, /data, and /cache are formatted as ext4. I'm not using any custom kernels, just what was included with the ROM. When I try to boot, my device momentarily sits on the "Your device is unlocked and can't be trusted" screen. Afterwards it reboots to the bootloader menu and then into TWRP. No matter how many times I try booting this cycle repeats. I think that maybe SuperSU needs an update to address Oreo compatibility issues. I really don't want to use Magisk.