It's night time in the states. The military try not to fly during these hours if they can help it, especially because of the dark and the restrictions on noise.

I noticed this happening even before the Capitol march, so whenever this happens I know that A. it's well past midnight in the U.S. and B. the military have turned in for sleep. They too need to sleep as well y'know, they can't be performing happenings 24/7.

Of course there could be flights without transponders for OP-SEC, but only if it's really necessary. And right now it's not (although it's close).

So best calm down. This is not a happening. What would be a happening would be seeing a dozen flights or more of C-130s and C17s at this time, and all destined for maybe Andrews AFB. Then you can say there's a happening.