Power BI embedding issue

We have embedded the Power BI report in a Web app using iframe and to give the access to the user we have created security groups. The user who have joined the group should be able to view the report in Web app. Sometimes user is able to view report but other times instead of report being rendered user gets request access button. If we click on the button power bi service opens where the user can view the report. This behavior is not consistent as sometimes report in loaded in the web app and sometimes request access button gets displayed.