We are currently testing latest mailman suite and notice that the requests API call will timeout if there are a number of pending requests.
Since the latest Postorious allow unchecking Pre confirm and Pre approved during mass subscribe, our support staff tried to add large number of email addresses to the list. We then found that we cannot click into the list from the web UI to administer it and an error message showing that "Mailman REST API not available. Please start Mailman core." Further checked that the requests API call failed to complete when we click the list on the web interface.
Looks like the UI should not try to load all the pending members just for the sake of showing the number of pending requests. Of course in normal situations, there should not be that many pending requests.