I would suggest you've got a PHP issue then because stdClass is a part of the base PHP API and class names in PHP are case insensitive (only autoloaders seem to enforce a case sensitivity).

php issue only for newly entered php 7?

why is it even looking in the mysqli.php file if this is a sql server install

a complete mystery

I ran into the same issue. The problem is that 'stdclass' is being passed as a parameter to the mysqli_fetch_object() which is then causing an error because it should be 'stdClass' and not 'stdclass'. To fix the issue, I did added a line of code in the /libraries/joomla/database/driver/mysqli.php file on line 886 that corrects the issue.

protected function fetchObject($cursor = null, $class = 'stdClass')
{
   if($class == 'stdclass') $class = 'stdClass';
   return mysqli_fetch_object($cursor ? $cursor : $this->cursor, $class);
}

That really shouldn't be necessary. Class names in PHP are case insensitive. I honestly suspect there is some environmental issue at play here and that there isn't something that could be patched in core to fix.

I can not replicate it.

1. On which version (full) of php the error occurs?
2. Which extension generate that error?
3. Can you replicate it in a simple script as below?
4. Does the error occur if you replace 'stclass' with '\stdclass'?

Example:

// Load necessary libs
require 'console.php';

$db = JFactory::getDbo();

$db->setQuery('SELECT * FROM #__users');
$row = $db->loadObject('stdclass');

print_r($row);

We ran into some other issues. We thought these issues were related to PHP 7, so we moved back to PHP 5.6. We then setup the same site in a dev environment and could not replicate the issue. We then upgraded the site back to PHP 7 and all works well. The issue is not arising. I am not sure why. I wonder if something in the opcache was causing a conflict that stopped once cleared.

OK - closed

Unfortunately, this error surfaced again. This time, I used opcache_reset() to clear the opcache and the error was resolved. This would indicate the problem exists within the opcache. I have yet to figure out how to reproduce the error.

It may solve your problem #14137