Translation:I have not been meeting my friends.
Encontrar is mainly to find, objects, hidden or lost things, or even hidden or lost persons. Same meaning as "achar" (when it's not to think).
But, encontrar pessoas is more commonly used to mean "meeting people".
Tenho um encontro: I have a meeting/date. Of course you could have been finding your friends, but that's a little unusual. Have been meeting is a lot better.
The hints give the general translations of a word, like a dictionary does. Only a dictionary is generally more complete. But not every translation applies to every contect and it is part of the learning experience to learn which translations do apply and which ones don't. With Duolingo most of the time the first translation is appropriate but sometimes none of the hints apply. In that case you can report it.
"Tenho tentado, mas não tenho encontrado nada."
Here, "não tenho encontrado nada" means in english "I have not been able to find anything" and you will get it wrong if you do not put this..
So in this lesson, I wrote, translation "I have not been able to meet my friends" and got it wrong...
Can anyone help clear the air on the difference?
"I have not been meeting my friends" = Eu não tenho encontrado meus amigos
"I have not been able to meet my friends" = Eu não tenho conseguido encontrar meus amigos
I haven't seen the other question you are mentioning so I can't comment on it, but "haven't been doing something" has a different meaning than "haven't been able to do something" in both English and Portuguese.