SOLUTION:
Hey guys I hope its not too late for the solution. I got these last year and I got to experience the same problem. Either one or both the earbuds don't charge.
If they dont get connected
The solution is just take both of them out. And pick any one, e.g you pick up the left one, you have to put it in the right bud's place. It has magnets so it repels but you just have to make sure with a little force that the metal contacts on both the case and the bud touch each other for a second. Once its done, put it in original position and it will work 100%.
It's weird but somehow it helps the current flowing again or it reminds the case to start charging the buds. BUT IT WORKS!