Joy-Con L doesn’t work properly

My left joy-con was so unresponsive at certain points that it become unplayable, but her left joy-con on the same Switch was literally perfect the whole time. This wasn't a case of it not working when I held it behind my back, I was literally 4 feet away with direct line of sight to the switch. Based on the fact hers worked flawlessly and mine didn't, it seems to indicate only certain batches are affected. I absolutely love the Switch so far, but I really hope Nintendo recognise this issue, and people who have controllers that aren't affected (like my girlfriend) do not try and convince everyone, including Nintendo, that we are just using it too far from the TV or that we have something in the house interfering with signal. As far as I'm concerned, what I've described above is proof that there really is an issue with SOME of the left joy-cons.