It is indeed odd that you no longer have the customize link in your overview tab.
According to the code, the 'customize' link will not be displayed if any of the following conditions is true:
a) the tab is not called overview
b) the user that's logged in is not a communityAdmin
c) there is currently another user editing the community (in which case overview page would be replaced with a notice that someone else is currently modifying the page.)
Do you have any customizations that might have changed any of these? Are the permissions properly set for your user? Are you running on a clustered environment?
It also might be as simple as a page error -- usually an icon will display indicating that there is an error in the page on the bottom right of your browser. It could be a browser incompatibility -- which web browser are you using to look at the page?
As a workaround in the meantime, you can put this url into your browser, and it should get you there: