Please provide a full reproducer.

<?php
error_reporting(E_ALL);
set_time_limit(0);

ini_set('memory_limit','2000M'); 
ini_set('display_errors', true); 

$dbo = mysqli_connect('localhost', 'xxx', 'yyy', '');
$dbo2 = mysqli_connect('localhost', 'xxx', 'yyy', '');

mysqli_report(MYSQLI_REPORT_ALL & ~MYSQLI_REPORT_INDEX);


$req = $dbo->query("SELECT * FROM mustBeATableBigEnough", MYSQLI_USE_RESULT);
$numFound = 0;

while ($found = $req->fetch_assoc()) {
    $numFound++;

    $req2 = $dbo2->query("SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID = '".$dbo->thread_id."'");
    if ($found2 = $req2->fetch_assoc()) {
        print_r($found2);
        $dbo2->query("KILL ".$found2['ID']);
    }
    $req2->free();
}
$req->free();

echo 'numFound : '.$numFound."\n";



it outputs :
Array
(
    [ID] => 2348965
    [USER] => yyyyy
    [HOST] => localhost
    [DB] => zzzzzz
    [COMMAND] => Query
    [TIME] => 0
    [STATE] => Sending data
    [INFO] => SELECT * FROM xxxx
    [TIME_MS] => 1.708
    [STAGE] => 0
    [MAX_STAGE] => 0
    [PROGRESS] => 0.000
    [MEMORY_USED] => 212672
    [MAX_MEMORY_USED] => 212672
    [EXAMINED_ROWS] => 0
    [QUERY_ID] => 554751313
    [INFO_BINARY] => SELECT * FROM xxxx
    [TID] => 3625133
)

Warning: mysqli_result::fetch_assoc(): Error while reading a row in ....testBug.php on line 54
numFound : 52


the table contains millions of entries

Oops, some autocomplete messed things up. I only wanted to change the status to Verified...

After looking a bit closer, I believe the key problem here is that this is calling a method on mysqli_result, while the error is reported on the connection (or stmt) and the result doesn't have access to the connection.

So either we need to store the connection object in the mysqli result object, or we need to recover it from the underlying driver -- mysqlnd has a conn field, which stores a reference to the connection data, so we could use the low level API to access the error information.