I've been clicking around for this stuff and it is happening a lot all over. So who is doing this?
It's almost to the point that we should be hoping it isn't human because they are flying/hovering them over neighborhoods, over military installations, etc. and we supposedly don't know where they are coming from and where they go afterwards. If this is a government doing this, then they might have a significant tech advantage.
Only options I can think of
1) non-humans
2) adversary country, Russia or China
3) our own country
The reason I think these are the only options is because it doesn't seem like these could be civilian drones because of their size, the length of time they are in the air and the fact that they aren't able to track them.
Non-humans, they would be doing this for a reason, whatever that is.
Adversary country, that would be really ballsy and provocative for them to do this.
Our own country, to do this and rile their own citizens up, the only reason to do that is for nefarious reasons.
I can't find any information that this is happening to Russia or China (though that doesn't mean it isn't), so if it isn't I think that makes it seem more likely that it is one of them doing it. It seems like if it was non-humans they would be giving this message globally.