TAB, Caps Lock, Space Bar and Delete intermittent operation
Hi, I have a Mac Air (mid 2012) laptop with OSX El Capitan V 10.11.6 and the TAB, Caps Lock, Space Bar and Delete all occasionally stop working at the same time. When this occurs, if I hold one of these button down for about 5 seconds they all start working again. The laptop has not suffered any damage, had anything spilled on it, and a hardware check in accordance with the link below revealed no hardware issues with both an short and extended test. There doesn't seem to be any obvious reason why they all stop functioning, but it's occurring about every 3-4 minutes. Any ideas??
https://support.apple.com/en-au/ht202731
MacBook Air, OS X El Capitan (10.11.5)