I have same issue and had been researching 2 month for this, however in my case, the Ctrl, 5, 6, -, =, F1 keys is delay on response, it needs 10 second of push to get actual response. My laptop is Lenovo Yoga520
Have been try with new OS reinstallation, driver update, vga update, bios update, other software/firmware installation, and nothing works, problem still there. So according with my case, if all soft method is tried and nothing worked it probably caused by phisycal problem on the laptop. I confirm this after do disassembly of the laptop and observe the laptop keyboard flexible wire connection. The flexible wire connection of laptop keyboard to connector plug on laptop motherboard is supposedly straight, so what i saw is : flexible termination at connector is slightly bent in corner, because flexible wire output on keyboard is not strightly aligned with the input connector in motherboard. So it need certain folds of flexible wire so the end of flexible wire connector is must be sraightly and perfectly aligned with connector on motherboard.
After i try this, my keyboard broblem is solved, now i can type all keys especially Ctrl keys :).
Be warned if you do this on your own it might break the warranty, mine is already broken because memory upgrade.
If you want you may get help with lenovo technical support team to investigate. I still dont know why lenovo not placing conector straight, or the keyboard is missmatch on conector placement.