Some people as you know have been having issues with the connectivity of the left JoyCon at certain distances and depending on how you grip it. Antenna-gate anyone? Sadly however, it looks like it's a hardware issue.
But fear not, Spawn Wave - a very handy youtuber set out to fix the left joycon antenna issue and not only did he fix it, he made it remarkably better! And with little more than a piece of wire and a blob of solder, the connectivity issue seems to be gone completely regardless of how far away you are or how you grip the JoyCon (within reason of course.) We don't recommend doing this yourself unless you have experience with this sort of thing, but let's take a look!
[spoiler=Shadows Original Post]So people have been complaining about the disconnect issue with the left JoyCon (personally, I've never run into this issue), but SpawnWave has done a tear down of the JoyCons and has now documented via youtube his experimentation with fixing the left JoyCon issue (he does have success, but emphasizes not trying it at home).
Unless you have a pretty in depth electronics knowledge/skills with soldering this isn't exactly viable for most people, but it is interesting and points to the culprit of the disconnect issues (the antenna placement).
Anyway, watch for yourself!