First be sure to type the full
admin@domain.com when you attempt login.
The admin accounts/the admin console already should revert to local, but let's go ahead and try zimbraAuthFallbackToLocal across the board:
zmprov md domain.com zimbraAuthFallbackToLocal TRUE
or
zmprov mcf zimbraAuthFallbackToLocal TRUE
(you'll of course want that back off, but this is just a test)
To be doubly sure it is an admin account:
zmprov ma
admin@domain.com zimbraIsAdminAccount TRUE