I just updated our discourse instance to the most recent updates, and noticed when trying to create an invitation link that I could not select a group for the respondents to be included in. Here is the error from the console that was logged when I clicked the option.
Edit: I’ve just tested both of these issues on my local site that is running the latest Discourse code. Both dropdowns that you mention are working correctly for me now. Can you try updating your site to the latest version of Discourse and see if that fixes the issue for you?