What is wrong in the elementary code for finding the maximum palindrome?

Question

Programming

Task: find the maximum palindrome substring in a string. Those.
Input data:

"wow"

Output:

"wow"

Input data:

"123wow123"

Output:

"wow"

Input data:

"abcdebob"

Output:

"bob"

Input data:

"rokor aba"

Output:

"rokor"

My solution that fails one hidden test:

bool isSubstringPalindrom(const std::string& str, size_t pos, size_t length)
{
    for (size_t i = 0; i < length / 2; ++i) {
        if (str[pos + i] != str[pos + length - i - 1])
            return false;
    }
    
    return true;
}

std::string getStringWithQuotes(const std::string& str)
{
    return std::string("\"") + str + "\"";
}

std::string longestPalindromeSubstr(string s) {
    if (s.size() < 3)
        return getStringWithQuotes("");
    
    // remove FUCKING quotes
    s = s.substr(1, s.size() - 2);
    
    for (size_t substrLength = s.size(); substrLength > 1; --substrLength) {
        size_t substringsCount = s.size() - substrLength + 1;
        for (size_t i = 0; i < substringsCount; ++i) {
            if (isSubstringPalindrom(s, i, substrLength))
                return getStringWithQuotes(s.substr(i, substrLength));
            std::cout << s.substr(i, substrLength) << std::endl;
        }
    }
    
    return getStringWithQuotes(s.substr(0, 1));
}