Spawn Wave's video shows how simply soldering on a piece of wire as an improved antenna seems to completely alleviate the Switch's Joy-Con connection issues.
If there's one major complaint that has been consistent across almost all the initial reviews of the Nintendo Switch (including ours), it has been the way that the left Joy-Con seems to have trouble maintaining a consistent wireless Bluetooth connection at certain distances. Now that the system is out, a YouTube hacker has opened up the controllers and discovered a design issue that seems to be causing the problem, and he even came up with a fix.
Spawn Wave Media's Joy-Con teardown video goes into significant detail identifying the various parts of both Switch controllers. The key bit, though, starts around the 20-minute mark, where the left Joy-Con gets opened up and the hacker says he's "not seeing any real antenna on this board." That's a bit of a surprise, since the right Joy-Con, opened earlier in the video, featured a dedicated antenna connected to the board via a small cable along the inside edge of the controller (where the tips of your fingers grip the controller). Then again, the right Joy-Con is laid out differently from its sibling (with the analog stick and face buttons essentially flipped) and sports an IR sensor on the bottom, so there is some potential reason for the change.
A bit more inspection shows the left Joy-Con does sport a Bluetooth antenna that's built into the circuit board itself, running up the top outside edge of the controller. That's right next to where the controller usually rests in your palm, which could cause your hand to block the Bluetooth signal quite easily. And while Spawn Wave notes that the PS4 has a similar on-board Bluetooth antenna design, the Switch's left Joy-Con antenna differs by "sitting next to a piece of metal" holding the circuitry for the Joy-Con's analog stick, possibly causing more interference.
from This could be why the Switch’s left Joy-Con has so many connection problems