Unable to add user inside Office 365 group from SharePoint

I have this weird problem, where we have a modern team site collection >> and using the office 365 admin >> I want to add a user to the underlying Office 365 group >> so I went to SharePoint site >> clicked on "Site Permission" >> "Invite Users" >> "Add members to group", as follow:-

but i did not get any option to add the new user, as follow:-

Also when i went to the Office 365 group and added the user as Members >> wait for around 3 hours now >> the user did not get any permission on the SharePoint site..

so not sure what is going on? Thanks