A community for the mobile app Connect for Lemmy.
Temporarily turning off unicode filtering may work if the users display name is different. (Some users may not be aware of what is causing this problem, unfortunately.)
(Maybe putting brackets around [usernames] might allow the "blank" usernames to be clicked.)
Tap on their comment, click on the person icon that pops up under the comment.
Then you will be on their profile page and can block them from there.
Oh. There is that. Derp. Tweaked the post and hope not too many people saw the error of my ways. :p