FINAL: The problem does not come from the assignments of the keys in Arm.a 3 or in Argo, nor even deleting the folder Argo in the folder of Arm.a 3.
The solution was as simple as changing the USB port where the keyboard was connected. I fail to understand that such nonsense will affect both the behavior of the game. Thanks for the attention, and if you think that you should not investigate more, close the ticket.

ADDING: More videos of the problem.

ADDING: reinstalling the game does not solve the problem.

ADDING: I have just discovered that if, for example, I hold the tab key to see the score, at 3 s it starts to blink in the same erratic way as when I hold the "shift" key. It happens with any key that shows "something" on the screen.

I use the translator now to make a conversation more fluent, so I ask forgiveness for the inconsistencies that this text may have. I have done data verification and nothing has changed. Before playing Arma 3 and flipping the keys of this one, Argo worked without problems.
Try, in Argo, to change to the default values ​​of the keys but this does not solve the problem.