I've had 3 cases of mobile account users on High Sierra (10.13.3) changing their Active Directory password then finding the password doesn't get updated for FileVault. I've had no such trouble on Sierra. The updated password works in macOS once FileVault is unlocked by another user. The only workaround we've found in to remove the user from FileVault and add them back again.
Has anyone else seen this, know if it's fixed in 10.13.4, or have any other workarounds?