Are you logging in with some sort of single sign on? If so, you'll likely have to adjust the java actions for your request handler to pass along the deeplink after login. We've done something similar before with Azure Oauth, but I'm sure it can be done with other SSO providers as well.
With the deeplink module, it was originally possible to use mxrequest.getParameter to get the parameters in your URL. Since the new microflow URLs no longer use parameters, you could instead use mxrequest.getResourcePath() and send that (or a substring of it) along with your request.