Added AD Groups are unable to access the site

Hello everyone,

Lately, I've been having this problem of having users who are getting access denied on the SharePoint sites, not unless their users' accounts are added individually into the SharePoint Group (i.e. Members with 'Contribute').

So, what happened is that on the ROOT site, I have added the AD group into the SharePoint group (with 'Contributor' permission) but they are still not able to access the site. Later on when I do a check on the site, I managed to find their user's name on the site but only with 'Limited Access' under 'Style Resource Readers'.

I went around to check for other solutions. I'm pretty sure this should not be the case because I did the same thing with adding AD Groups into SharePoint Groups for other SharePoint sites (not under the same farm) before and it works properly (even when I add new staff user into the AD Group, that user is able to logon to the site).

Any idea to this issue? Or any terms to suggest to search close to this solution.

Thank you and Regards,

Kristen