1. Lots of people staying at home.
2. Lots of people out of work.
3. A challenge to the authority of the police to conduct society(the virus is more threatening than they are, and populations are resisting the return to business as usual narratives)
4. A lack of targets for police harassment to "let loose on" (because nobody is out and about)
These factors all build up to make a tinderbox where the officers who are looking for trouble(and they are always present and hungry for action) go out of their way to stir it up through provacateur tactics, and the population responds with quite a lot more force than usual since they are out of work and stuck at home and have nothing else to do. And it only escalates from there, because, again, you have police officers that are really dead set on the idea of "go get 'em", and see this as a role-playing opportunity. I should discuss the role-play in some more detail.
In the decades of collective memory, protests served as media flashpoints where the action is molded to the narrative. Everyone involved does a little bit of role-play, gets their fill of the narrative they want to see, and then goes home, with a few arrests and a bit of violence along the way, and a media product is subsequently served on the news afterwards, shaped to fit the tastes of the audience. Career activists would develop personal brands around the appropriation of protest groups towards news narrative, and the police were eager to play along and be the "other side". This dynamic of protest-as-product made protests seem unable to address legitimate concerns, since neither group was "going for the throat", as it may.
The dynamic has gradually shifted, at first slowly with protests like '99 Seattle WTO, and then faster as you get into the 2010's and live streaming takes off; coverage is getting much closer and more personal, and this runs in tandem with the rise of surveillance and police militarization creating pervasive cynicism about large institutions of all kinds. Branding of all kinds - from CNN to the blue check mark Twitter account - is mistrusted. Direct action is increasingly tolerated by the population, who can now easily hear the case for such without an intermediary. The virus has accelerated those trends, and so there's a sense of nobody holding back anymore.
Which, of course, makes it easier for the police to dehumanize the protestors.