"The redirect URI included is not valid." after mmost URL change

Hey, this issue has popped up here and here, but neither have answers that apply to me (I don't think.)

I don't have a proxy in place, and I'm at the current version, so I can't update right now.

GitLab 8.4.4

I changed the url of mattermost from old.mydomain.com to new.mydomain.com in /etc/gitlab/gitlab.rb

mattermost_external_url 'https://new.mydomain.com'

When I go to https://new.mydomain.com/myteam I get directed to the correct "Sign in to myteam on gitlab mattermost 'with gitlab' ". When I click Sign in with gitlab, I get directed to the Profile Settings page with this error "An error has occurred, The redirect URI included is not valid." I did run gitlab-ctl reconfigure after the change to gitlab.rb. Not sure what else I can try right now. Any ideas?