It's no secret Nintendo Switch has experienced some minor hiccups since launch, a fact not forgotten by those affected despite the system's so-far stellar sales. In particular, an issue with syncing and wireless signal of the left Joy-Con had repeatedly cropped up, and today Nintendo saw fit to comment on the issue and offer an explanation.
In a statement to Kotaku, Nintendo had the following to say:
We have determined a simple fix can be made to any affected Joy-Con to improve connectivity.
There are other reasons consumers may be experiencing wireless interference. We are asking consumers to contact our customer support team so we can help them determine if a repair is necessary. If it is, consumers can send their controller directly to Nintendo for the adjustment, free of charge, with an anticipated quick return of less than a week. Repair timing may vary by region. For help with any hardware or software questions, please visit http://support.nintendo.com.
As Kotaku's report also notes, CNET appears to have inside info on what Nintendo's fix might be: attaching a tiny piece of conductive foam to the left Joy-Con. My own personal experience aligns with Nintendo's account as I've experienced exactly zero issues when it comes to Joy-Cons short of what you might commonly expect with a Wavebird gamepad or Wii Remote. In other words, pointing them directly toward your chair, at your leg, or into other obstructions does in fact block the signal.
Regardless, "manufacturing variation" does encompass issues of sporadic, inexplicable frequency, so Nintendo's explanation should hold just fine while they ramp up production. If you are having an issue, be sure to get in touch with them for some free foam (or at least, instructions on how to apply it).