The 2-to-1 decision is today's Feminist Majority Foundation v. Hurley (the University of Mary Washington case). I'm traveling, and thus won't have time to post a detailed analysis myself, but here's part of the analysis from Samantha Harris at FIRE:
The alarming upshot of the ruling is its suggestion that Title IX may sometimes require colleges to censor or block all students' access to certain internet sites or services based solely on anonymous statements made in an online forum that the university does not control, by people who may not be on campus, or even affiliated with the university at all.
The case ... stems from a series of events that roiled UMW's campus back in 2015. At the time, members of the UMW student group Feminists United on Campus (a local affiliate of Feminist Majority Foundation) were speaking out about several issues on campus, including the student senate's decision to authorize fraternities as well as a bawdy rugby chant that several members of UMW's men's rugby team were recorded singing at an off-campus party. Following their advocacy, FUC members found themselves the targets of online hostility, particularly on a now-defunct platform called Yik Yak that allowed users within a certain geographic radius to post anonymous messages. FUC complained about this repeatedly to the UMW administration, and after they found UMW's response to their complaints to be lacking, they first filed a complaint with the U.S. Department of Education's Office for Civil Rights and then, ultimately, a federal [Title IX] lawsuit....
In a ruling that has far-reaching implications for universities' obligation to monitor and address the off-campus, online speech of its students, the [Fourth Circuit] held that because UMW had the "technical capacity to control the means by which the harassing and threatening messages were transmitted" (that is, the ability to block campus network access to Yik Yak altogether) and because they could have taken other actions (such as "mandatory assemblies" or "anti-sexual harassment training") to make clear that sexual harassment by its student body would not be tolerated, the plaintiffs had sufficiently alleged that UMW had substantial control and thus could be liable for the harassment.