Why is Salesforce redirecting all my community users to the same user while using an external Identity identity provider?

Question

There is a Salesforce application with community users who have a landing page URL for which access needs to be provided to endusers through email which cannot be done. The requirement is for the enduser to make use of their phone number or employee id as they cannot have fresh email addresses.

When i try to connect the SFDC to my external IDP, it is able to go with the IDP for authentication and finally login to the application. However the user that is logged in always reverts back to a single user in the application though i make use of seperate logins for each time.

Ex: User login is alex12 and i login, it will take me through to the landing page in the community page. user login is mike23 and when i login, it will pass through fine but the landing page in the community page will still show alex12 instead of mike23.

What should i do to get all the users in community user to login and land on the community page successfully for each user?

Any help is appreciated as i need to deploy for a client and this on the escalation track.