I see, then that explains the 'de-sync' problem -- the left joy-con does not have an antenna!!! If so, it can be fixed, but I don't see Nintendo changing the design in the last one week since the problem was reported. They must have already manufactured tons of the switch and joy-cons. So the first batch will all have the issue until they make the design change. Note also that there is no provision on the left joycon to mod in an antenna (no slot next to the battery, no screw to connect an antenna), so sending it back to Nintendo they wont be able to fix it, only way is to replace with a revised version.
Actually it's very possible that only the right joy-con needs an antenna, becos only the right side connects to the Switch. The left will connect to the right (the distance will be closer), which acts as a middle man. Then the problem is signal between the left and right joy-cons being weak. If that's the case, there are a couple of ways they can patch it. Either strengthen the signal where left and right communicates (could be via FM) or add antenna to the left. (Actually FM makes sense, which could explain why some ppl have problem while some dont, cos interference could come from whatever radio stations exists locally.)
btw, Technically it is not de-sync. The joy-con is still sync'ed to the switch, the connection is not loss, as indicated by the LED light. But a lot of the signal sent from joy-con is not getting through.
. Always connect my wireless headphone directly to the console/pc so didnt bother to use the tv bluetooth audio. 
