Users missing in Author Dropdown Menu

I am using the latest version of the classifieds responsive theme and wordpress.

My issue is that when someone registers and posts a listing every time I approve the listing that listing is attributed to me.

Before I was able to assign any listing to any user using the ‘Author Dropdown Menu’ (see screenshot attached)but now the only user that appears is myself as the admin.

I have checked my list of Users from wordpress users menu and all the registered users are there so don’t know why they do not appear in the Author Dropdown Menu.

Does anyone know how to fix this? or point me in the right direction?