Using Ubuntu Mate 18.04. Whats happens is almost the same that was explained on this question:
"Basically, the keyboard will stop functioning normally and only register input if you hold a key down for two or more seconds. When you release the key, it stops right away like it should."
But, in my case, the keyboard is wireless (keyboard and mouse combo with the same wireless USB receiver).
How to investigate the root cause of this problem?
Already investigated and discarded possibilities
batteries: the problem occurs even with fully recharged and/or new batteries
changing USB port: changed the receiver to different ports, from USB 2.0 to 3.1, without success