I’m sure it happens somewhat frequently. I’ve heard some Title IX cases as a faculty representative at my institution - there hasn’t been a faculty-student case but I have heard a case about a graduate student having an inappropriate sexual relationship with a client. On the other side of this issue, FWIW, I exercise extreme care when meeting with students - I keep the door open and only schedule office hours when other people are around. I’ve contemplated whether I could legally record all meetings just to CYA myself in the event of a false allegation. Tenure doesn’t matter. Students have made sexual advances towards me in the past. I’ve either ignored them or one time I took it as an opportunity to discuss boundaries.