|It seems I installed Windows 10 in early May. I'm pretty sure this problem started in May or June.|
Sometimes a firm tap will do it, but mostly not. As I say, they can be working just fine for a while, and then just suddenly stop working. After a bit they may work again for a few minutes, then stop.
I saw on this forum another person posting about what appears to be exactly the same problem with the same keys on a Vaio laptop. Unfortunately, he asked for replies to his e-mail, so I don't know what help, if any, he received.