I've seen a couple of threads on this issue, but I thought I'd share a script that I use in Self-Service in case anyone has a need. There's interactive osascript prompts to revoke & reassign securetoken, and then update the preboot volume to resolve the issue. No need for fdesetup.
If you have a mobile AD user on Mojave and the password is reset off-device (like in AD/Okta/or a Windows PC) then the new network password never syncs with FileVault, and the login window password will sometimes revert to the "old" password if the user is off-network.
I'm also using LAPS at my org, so this script pulls the current LAPS pw from an extended attribute for use with sysadminctl, but you can easily take that variable out, if needed.
