macos, FileVault, and the Guest User account

I have two 2017 MacBook Pro's, both identical in spec and bought the same day. Both should have identical OS setups. The startup disk on both is "APFS (Encrypted)". Both have FileVault turned on. Both have the Guest User set to "off" in Users and Groups.

One computer, upon boot, only shows the single Admin user account.
The other computer, upon boot, shows both the single Admin user account AND the Guest User.

Any ideas what's going on here?