Hi,
The ideal behavior is not like this, ideally if from backend you set "Minimum of different classes" = 2 then it must show error while entering the password.
I tried the same in default Magento with same settings from backend on my account change password section and the error shown is "Minimum of different classes of characters in password is 2. Classes of characters: Lower Case, Upper Case, Digits, Special Characters.".
Please share exactly at which step you are facing this issue. As this is not occurring in deafult Magento I doubt if you have done any customisations regarding this ?
If my answer is useful, please Accept as Solution & give Kudos
Thanks.