By now we have all heard of the desync issues for the Nintendo Switch's left Joy-Con, and according to Cnet, it's a hardware issue, meaning that there's no software update coming to fix it.
The good news is that Nintendo seems to have found a really easy solution to fix the problem. The left picture shows a faulty Joy-Con, and the right photo is a fixed one. The only difference seems to be that small black foam square (conductive foam) at the bottom right, and removal of that foam causes the Joy-Con to stop working (again).
It seems that the newer Joy-Con models don't have this need for conductive foam, so Nintendo appears to have fixed the problem for future batches of the Switch. Have you had issues with the Joy-Cons, and have these issues been major?