After reading your initial post, I agreed with your conclusion that something was fishy. Nevertheless, I read the entire 68 page chat on Ms. Young’s website to confirm my own suspicion. I left her website scratching my head as to the how and why Ms. Young would manually fabricate such an intimate conversation and, in the process, append the mislocated [block user icon] to a small sample of her DMs. They are expertly placed and scaled and, as ‘K’ suggested in his reply, are consistent in appearance throughout the chat log. I also noted that the new anomaly you discovered also occurs throughout the screengrabs she has posted on her website. Nothing makes any sense.
For what it’s worth, I conducted my own deep search online to determine if there was a history of other DM users reporting the same bug. I found nothing. Until we learn more, I guess this will have to remain as another unsolved mystery just like Seth Rich’s murder and all the dark and bizarre events that frame it.