Cannot encrypt Nexus 6P with Marshmallow 6.0.1 after TWRP root and Xposed

I recently bought a Nexus 6P and I just rooted it a few days ago. I have been reading about how it is less safe now that the bootloader is unlocked, so I figured I could encrypt my phone for more securities! I don’t want ro re-lock since unlocking will wipe my data all over again.

So I went into Settings->Encrypt phone and started the encryption process. It first showed a green outline of an Android, then it started the boot animation. It stayed there for about half an hour and it was clearly not encrypting (not getting hot or anything) so I just rebooted (I have a backup, that’s why I’m so bold ) and it just normally rebooted to a working phone with nothing encrypted. Tried it again, same result.

I’m running Marshmallow 6.0.1 MMB29M with TWRP, SuperSU (I’m pretty sure it’s systemless) and Xposed. I’m not sure what kernel I flashed when I rooted (that is the boot.img, right?).

Is this a bug? Is it a feature? I would like to be able to encrypt my phone; does anyone have any ideas on how to achieve this, now that TWRP can decrypt stuff?

Thanks!