127.0.1.1 is used in ubuntu / debian by default in /etc/hosts for fqdn.

Due to the fact that address don't literally match the address of network interface isLocal fails to detect that address as local.

See
https://www.debian.org/doc/manuals/debian-reference/ch05.en.html#_the_hostname_resolution
https://serverfault.com/questions/363095/why-does-my-hostname-appear-with-the-address-127-0-1-1-rather-than-127-0-0-1-in

https://github.com/ClickHouse/ClickHouse/blob/51ba12c2c3106d9277bbc223adfe41fdb3e45439/src/Common/isLocalAddress.cpp#L13

#include <gtest/gtest.h>
#include <Common/isLocalAddress.h>
#include <Common/ShellCommand.h>
#include <Poco/Net/IPAddress.h>
#include <IO/ReadHelpers.h>
TEST(LocalAddress, SmokeTest)
{
    auto cmd = DB::ShellCommand::executeDirect("/bin/hostname", {"-i"});
    std::string address_str;
    DB::readString(address_str, cmd->out);
    cmd->wait();
    std::cerr << "Got Address:" << address_str << std::endl;
    Poco::Net::IPAddress address(address_str);
    EXPECT_TRUE(DB::isLocalAddress(address));
}