I think there are two separate threads running through this. One is his academic criticism of their work through the academic publishing process. I hope no one

I think there are two separate threads running through this. One is his academic criticism of their work through the academic publishing process. I hope no one would describe that as 'harassment', irrespective of how much his academic output focused on challenging their work. The other is his extremely poor and possibly slightly autistic Slack behaviour, fixating on his disapproval of their work and repeatedly bringing it up in even the most marginally related contexts. That part I would agree rises, or at least arguably rises, to the level of harassment.