Hi can you please provide more details? Are you missing details for real user monitoring or synthetic browser monitors? If you have an account please open a support case, this might be the right channel for your issue.
Is this Login page delivered by the same server which is delivering the rest of the application? If it is a different server make sure it is also instrumented with the OneAgent to get the JS Agent at the login page.
AFAIK single page requests are not counted reported to user sessions. Unless to session proceeds to other pages, it's not reported as a session for licensing.
You are correct, it's visible as a session in Dynatrace, but it will not be counted for licensing (bounce visit). Sorry, it was my misunderstanding.