numeri al contrario

By backwards you mean a 3 would be flipped so it's like this: Ɛ, right?

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

It's a mater of focus. You lose focus after typing in the first 3 digits. Do you pause after the third number? I have the same problem in Contacts when I try to enter additional data in a contact card. If I pause then the focus is lost. Haven't found a solution for that yet.

Next time please run your reply thru Google translation and post in English. Thanks.

Can you type in some numbers as an example?

Where exactly are you inputting this code? Which app, which web site?