There's a reason why the Nintendo Switch's left Joy-Con is the one giving people trouble.
Before the Nintendo Switch launched last Friday, a number of reports from the press with early access to the console mentioned desync issues with the Joy-Con controllers. Specifically, the left Joy-Con.
Some hoped the problems would be alleviated with the day one patch, while others believed it to be the result of a Bluetooth signal loss that's likely hardware-related. Now we know this is indeed the case, and the reason why has to do with how Nintendo designed the controllers.
YouTube channel Spawn Wave posted a teardown video of both Joy-Con controllers earlier, confirming that there are differences between their internal components. Outside of the NFC reader and the infrared camera in the right Joy-Con, the teardown revealed another startling design flaw.
The Bluetooth transmitter inside of the right Joy-Con has a dedicated antenna, which means the signal is less likely to be blocked or interfered with. The left one, on the other hand, does not. Instead, the antenna in the left Joy-Con is soldered directly onto the motherboard, right next to a metal box.
This metal housing, combined with the fact this particular part of the controller will be covered by fingers, result in weaker than usual signal. In some cases, it gets completely blocked, hence the issues reported while playing Zelda: Breath of the Wild.
The video above explores a possible fixe for the problem, and shows how to do it. In this case, the solution was to extend the Bluetooth antenna by soldering a copper wire to it and putting the other end of said wire near the bottom of the controller.
After extensive testing, this DIY solution showed great results with a range and signal strength far exceeding that of the original, as well as the right Joy-Con. It goes without saying that this will void your warranty, so do this at your own risk.
If you're looking for fixes that don't involve taking apart your controllers, Nintendo posted a number of potential causes for Joy-Con connection and desync issues. Check the support page for more.