Python Password Checker - If statement not correct

I am trying to generate a password checker in python that uses the following rules to determine the strength of a user's password.

The user's password is WEAK if it is less than 6 characters long. The user's password is STRONG if it contains at least 13 characters, at least 1 lower case letter at least 1 capital letter and at least 1 numerical digit. The user has a MEDIUM password if it is neither a strong or weak password.

I have generated the following code:

def strengthOfPassword ( pass ):
    strongness = 0
    up = 0
    low = 0
    num = 0
    for i in pass:
        if i.islower():
            low += 1
        if i.isupper():
            up += 1
        if i.isdigit():
            num +=1 
    print (len(pass))
    if len(pass) >= 13:
        if up > 0 and low > 0 and num > 0:
            strongness = "STRONG PASSWORD"
    if len(pass) < 6: 
        strongness = "WEAK PASSWORD"
    else:
        strongness = "MEDIUM PASSWORD"

    return strongness

strengthOfPassword("2Benji3all4Kiwi")

The code works for most test cases, however for the string "2Benji3all4Kiwi", the code incorrectly states that this is a medium password, rather than a strong password, despite meeting all of the criteria for a strong password. Why is this?