The first thing to do is deactivate all other plugins and see if the activity page is loading. If it does, and it should, then it’s probably a conflict with another plugin. You can then reactivate the other plugins one by one until is stops working and you have found the culprit.
Another option, as I suggested, is to right click on the page, click on inspect and then find the option that says “console”. Here’ you might see some errors displayed, and this might give you some clues as to what the problem is.