Enemy champion invisible? 3V5?

Today I started a premade match, everything looks normal in the champ selection part and loading part.

But when I get into the game, I can only see three champions on the enemy side (by holding Tab), and I asked them with all chat. The mid laner replied me, however, his name is GREEN and there is no braket with the champion he selected, just his nick name...

I didn't notice that this player's name actually didn't appear on the board, thinking that this maybe a new mode? 3v5?

Of course I started normal farming, and... suddenly I was at low health... and a few sec later I was dead. Actually their mid laner Ahri was hitting me, but I have not warning redden sign, nor can I see her or her skill effect.

This is later fixed by reconnecting...but Ahri already got two free kills...