While there have been a number of reported issues with the Nintendo Switch, one of the most common seems to be how the left Joy-Con controller has issues with staying consistently connected to the console. It now appears that there could be a fix for the controller, but it won"t be an easy one.
According to the Spawn Wave YouTube channel, the right and left Joy-Con controllers internals are actually different and this is why maybe the left one has an issue staying connected. The right controller seems to have better connectivity because it includes a separate antenna, rather than the left controller that has its antenna built into the internal board and is in extremely close proximity to some metal shielding.
Naturally, not everyone will have the skills or courage to perform a mod like this, but if you"re up for the challenge, this fix might be for you. To put it simply, what is required is that a new antenna needs to be soldered onto the board of the left controller. This will allow for better penetration of the signal from the controller to the console. While the fix seems to improve the controller"s connectivity, you"ll have to perform the fix at your own risk and it goes without saying that this will void the warranty.
Source: Spawn Wave via The Verge