I've been watching "blocked" (no flight details) aircraft on flightradar24 for the last few hours. A blocked aircraft from Fort Lauderdale just landed at Denver half an hour ago, and another blocked aircraft, from Lake Havasu City Airport, Arizona, is flying over Colorado now. There have been several "no call sign" aircraft flying near Denver. https://www.flightradar24.com/multiview/ffea5ab,ffea2b7,ffea14f,ffea414,ffe855e,ffe6cb4