Yes, it's like that movie The Sixth Sense, when the kid says "Walking around like regular people. They don't see each other. They don't know they're dead. "

The issue is that italki doesn't inform them when they are blocked, and they can see their own posts, even while no one else can. Still, I can't believe some of them still haven't noticed that not a single person has responded to them.

Perhaps the problem rests with the website database. In the database are all the names of the members. When someone is blocked it is recorded in a list of blocked members. The website coding then scans their comments, determines that they are blocked, and prevents the comment from being shown. What the database doesn't do is block the reception/acceptance/inputting of the comment, but then blocks the comment from being shown. If the website's programming was robust enough, it would block the blocked user from even being capable of communicating with the site.

Now, if anthing I've suggested is invalid, I can only apologize profusely, and beg everyone's forgiveness, and simply say how very sorry this older gentleman [ :) Su.Ki.] is. But I'm not sorry for being Canadian, even though I am sorry for literally everything else in the world that has happened and/or could happen. I once told a waiter in a restaurant that I was sorry for asking him why my meal was taking so long to be cooked, ergo, I must be Canadian.

I guess Dave apologised because he's Canadian? Only Canadians and Brits apologise as easily as breathing. Don't be surprised if a British person says 'sorry' when you've knocked into them by mistake - we apologise for putting you to the trouble of having to say sorry to us!

I'm honestly confused like you right now (,") Because no way that some members are privilaged to see those invisible answers/comments and others don't! 

Unless the member who answered deactivated his/her account; which means he's not blocked and he answered the question, and after it was seen and checked as resolved from the OP, he deactivated his/her account again. Do you think it's possible Su.Ki.?

Yes, Su.Ki. I've noticed that! These are blocked members by italki, but sometimes they just don't know that they are blocked, because their comments are visible to them but not to us. Yet I suspect that some of them know that they're blocked and nothing from their comments are visible right now, but they are counting on the moment when italki unblock them, because all of their comments/ answers/ corrections are going to be visible again.