I got the Switch about six months after launch, and have had drifting issues on both the right and left joy-con. The right one started to drift a little bit about a year ago and then got better on its own, then the left one started in about six months later, right when I was in the middle of playing through Dark Souls for the first time.
And to anybody who says that drift doesn't make games unplayable, going through Sen's Fortress with a character that randomly decides to start walking to the left is pretty damn unplayable.
I managed to make the left stick drift go away with some contact cleaner, and I gave the right one a shot, just to be safe. Got a pro controller not too long afterwards, and haven't played much in portable mode anyway since apparently most of the people developing games for the Switch don't scale their text for people who are actually playing on the small screen (Helloooo Skyrim and Diablo 3!).