There's a bug where the tabs in the Activity screen overlap the badge tracker section and it hides the "Track the next one" link. Chrome 69.0.3497.100 on OSX 10.14 Mojave.
Yes, people have been noticing this on all sites throughout the Stack Exchange network. There's a 'central' bug post on the Main Meta which has now been marked status-completed, meaning it should be resolved.
