Problem:
I'll demonstrate the error with the modal Dialog "Add workspace permission". This issue can also occur with other Dropdowns.
Actually the loading image should be displayed and the templates should be loaded from server. However, there is no loading image to see and no templates can be selected.
This problem happens, because the SharePoint context is expired. We are already working on a way to solve this issue.
Solution:
You have to return to SharePoint before navigating to the page again. If the problem persists, consider deleting your browser's Cookies.