Azure OAuth: invalid client secret after this weeks updates

Got a big red error message after this weeks updates that says that the client secret is wrong.
But I havent changed it, it’s still the same secret in gitlab.rb, and one can’t change it in Azure AD …

Any ideas?

Update: Client Secret changed in Azure and updated in GitLab multiple times now.
Still the same error.

GitLab says it’s up to date with version v11.7.5 (c5b5b18)

What is going on?