Ever since the Switch started being used in the households of customers, there have been complaints about its wireless Joy-Con issues. Particularly on the left one, affectionately called left-con had problems with losing connections. Though sometimes both the joy-cons have this issue. There has been some attempt on DIY fixes as well. Nintendo may have found out what is causing these problems according to the statement given to Kotaku by Nintendo.
“There is no design issue with the Joy-Con controllers, and no widespread proactive repair or replacement effort is underway. A manufacturing variation has resulted in wireless interference with a small number of the left Joy-Con. Moving forward this will not be an issue, as the manufacturing variation has been addressed and corrected at the factory level. We have determined a simple fix can be made to any affected Joy-Con to improve connectivity.”
This statement coincides with something Sean Hollister from CNET noticed after Nintendo made a quick fix to its faulty left Joy-Con. He took before and after pictures and he found out that the only change made was the addition of a bit of conductive foam. Which is added possibly to shield the joy-con from any kind of interference. Also, some new controllers brought from Amazon sported a circuit board with a different manufacturing code and lacked the modification. If you’re having problems then you should contact the company and get the fix.