Hi,
When I login I only use the username without domain.
I try without filter and I changed my baseDN for different thing. I tried the full basedn, only dc like you see in my current config. I also tried with the default CN "users", I moved one user there and try to login with and doesn't change anyting.
I reset the passwd on the user I use for my test to be sure. I tried to make him domain admin. But I always have the same result. It always said the user is not registered. I even try with a new user I created only for testing mattermost.