Happened to me quite a lot.
Anyway, glad I found this topic, because I wanted to ask about this as well.
I could use the pictures on the left side to target, yes, but for example in pvp it's just too many. I want to target my closest ally.
F2 for me doesn't work, because I play on a laptop, and to activate F2, I have to use another special key, otherwise that button would just change my screen brightness.
So I went to the settings to change key binding. I choose "T" to target my groupmates, but in the game it won't work. I tried to check maybe T is associated with something else, but it's not the case.
So now I'm not exactly sure which key I could bind for this...