That might be a difficult one to get an answer to from a contemporary "anarchist communist". When I identified as an anarchist communist, I hardly agreed with the general consensus. But the practice that time was often built on top of Anti-Racist Action and its ethos. The practice I was exposed to was to beat up people they thought would be violent or even snitch on them, as a group. For sexual violence, since most were women, I imagine they could've thought something up to respond to that.
In formal practice, there has been activist courts called, public letters written, all sorts of things to justify any action that seemed like the handling of an internal problem. For things outside of this, typically no one calls anyone out on it. They just tend to be alienated, then move on to other things.
I didn't write this as an answer since my anarchist communist experiences are outdated.