It looks like a user deleted their comment, causing the subsequent responses to not be shown. When I view the post from my admin account it's all still visible to me (see the screenshot below). Though if I view the post from a non-admin account then the deleted comment and all its children are not shown.
I agree that this is weird behavior, but I think it's by design. In this case I would prefer that Lemmy show everyone the "deleted by creator" note and keep the rest of the comment chain visible. I am not aware of any server or community settings to change this behavior.