Based off your screenshot it seams like it's trying to display activity, but it can't find any. It'll attempt to fill out a page by looping the query, but it'll take a really long time like that if there's nothing it can display. This happens with server side aggregation.
I can take a look if you PM backend super user login credentials as it could be a couple of settings causing it to get stuck like that. Will also add a feature ticket for it to give up sooner if it can't find anything.
forge.joomlapolis.com/issues/9407