Could not connect to a virtual terminal – repeated return?

My Ubuntu 18.04.2 system is working properly, except for the following problem:

I can not connect to any of the virtual terminals (Ctrl + Alt + F1 to F6.) Specifically, I know how to type my user name correctly and the keyboard works without any problem, without unusual behavior, up to That I press Back (or Enter on the keyboard).

At this point, the password prompt appears but immediately, it's like pressing Enter again. It is therefore necessary to enter a blank password and to indicate that Login is incorrect. The login prompt reappears, but again, it's like pressing Back immediately, again giving a connection error. Repeat it several times until the screen clears and the login prompt is displayed again. Now, Return does not keep repeating.

Ideas? The Back key works well in graphical mode.