The usual suspect for a keyboard malfunction is corruption of the RAM section where the keyboard buffer lives. This can happen if another program overwrites part of the buffer. Deliberate "overstuffing" a buffer is a common way of exploiting vulnerabilities to get malware on a computer, but the keyboard buffer space is "reserved" so it's unlikely that malware would access that region of memory.
It occasionally can happen with an intermittent connection of the keyboard. A wiggly connector, or a cable that the cat's chewed on can do it.
Some "modern keyboards" have bunches of extra switches and rollers and cranks for doing exotic things. Any "stuck" key, or a noisy pot on a scroll wheel, or a bit of fur and feathers in the optical path of one, could be a cause.
Wireless and/or USB keyboards require drivers that sometimes have problems that seem a bit like "memory leakage" where the buffer isn't cleared completely when it should be, so the next keystroke isn't properly read by the driver.
USB keyboards may have a problem similar to one found with USB mouses, where an input while the computer is entering a "sleep" or "standby" mode doesn't get completely transmitted. When the computer is called back to active mode the USB drive can't be properly initialized because it's still "waiting" for the rest of the previous input.
But mostly it's pixies, elves, and gremlins, or fat 0s and bent 1s. I think I've also heard of "wrinkly 0s" that don't flow well. The cure suggested was to breath fumes of your favored (and best) beverage across the keyboard to "plump up the 0s." It may not work for the keyboard; but might make the driver happier.