On an Acer laptop running Debian 10.4, occasionally a few keys stop working. It is a few keys stopping to work for weeks, others for days or hours, or only for a few minutes.

The laptop is five years old and I tried to clean the keys underneath with an air duster but this doesn't help. It could be a mechanical problem in conjunction with corrosion, I assume. No key so far stopped working for ever.

The only thing, I don't understand is this:

Often, only capital letters don't work. That means, shift + r doesn't work ten times in a row, but r as minor letter works, all the time.

What also works, is caps lock + r, all the time, producing a capital R.

Why does work, the r key only, caps lock + r, too, but shift + r not? The shift key itself is working with all others key, instead. All the time.

Can someone explain please, why this should not be a software issue? I have no idea of what piece of software could be responsible for that, but it sounds rather strange to me.

All this behaviour seems to be independent form any application and I am using the command line program xev to test the keystrokes.

It sounds like a mechanical problem to me. Can you pry of the offending key caps (including the shift key) and clean out any dust or debris that might have accumulated?

If something has gotten under a key cap, it's entirely possible it might move around, accounting for the intermittent nature of the problem. Compressed air by itself might not be enough to dislodge it.

You might also boot to a Live CD/USB of some other distro and test (you would have to stay in live mode for a reasonable amount of time). If the problem does not appear, it might be a software issue, but, frankly, I've not heard of a software issue of this nature since I first started using computers in the DOS 3.2 days.