Value that occasionally enters HTTP_X_FORWARDED_FOR

Obtain the client ip address via the AWS load balancer using the following methods:

$ips=isset($_SERVER['HTTP_X_FORWARDED_FOR'])? $_SERVER['HTTP_X_FORWARDED_FOR']: false;
if($ips){
    $ip =explode(',',',$ips)[0];
}

This $ip has a 99% chance of getting the correct value, but a little less than 1% chance of getting the following format.

xxxxxx xxx.xxx.xxx.xxx 
// x is all numeric, (6 digits) half-width space (ip address)

Six digits do not seem to have any particular regularity, some starting with 00... and some starting with 90... (if I may say so, many starting with 0... and others starting with 9...)
Also, the ip address at this time is a private address like 172.31.xxx.xx.

If anyone knows what the situation is like, could you please let me know?
Also, what is this six-digit number?
Can I get the client's ip address at this time?
Thank you for your cooperation.