Can't target NPCs

[Ukase]

So..I was listening to YouTube in the background while I was playing. Got on a PUG for the Abandoned Sewer Trial, and in the midst of a fight - I could no longer target any rikti. When I tried, I would target the nearest teammate instead. (thankfully, it wasn't any kind of confuse, because my attacks didn't go off) 

I mention YouTube, because I was about to log off and re-validate, but figured I'd close YouTube first - and suddenly things returned back to normal so I didn't need to do anything. 

This had happened before, but when I was running a second account - I figured some pixel wires got crossed, and it went away when I shut down the 2nd account. 

I suppose this could be a memory issue on my end, but only because anything is possible - but I don't think it's likely.