Cannot login using SAML-based authentication

I am attempting to configure SAML-based SSO for using AzureAD, following the GitLab documentation at:

against a new group and AzureAD configuration; eg using user.objectid for matching.

I have also configured SCIM Provisioning to create the user that exists in AzureAD in GitLab; this process completes successfully.

When I attempt to log into GitLab via the SSO signin URL, I am prompted to enter my AzureAD credentials as expected. However on successful authentication my browser is redirected to the Git Login screen, which includes the message banner: ‘Login to a GitLab account to link with your SAML identity’

Has anyone had experience with this, and able to provide any hints as to the issue or how to find the cause? NB A 2nd SSO-defined user does work; I believe it became linked with my original GitLab account on its creation.