Autoloader not finding classes from my plugin

Given the first PHP code snippet you posted, I don’t see that you’re using the class yet, which explains why you’re not seeing your classes in the autoload error log that you’re debugging with.

Note that use will not trigger PHP’s autoloader.

use My_Plugin\Includes;

You need to actually instantiate a class, check that it exists, or do something else that requires the class to actually be loaded into memory at runtime. Only then will the autoload queue receive a request to load one of your class files.

As it stands, the only class you’re using is the Autoloader class itself, which doesn’t need to be autoloaded, because you’ve included the class file explicitly.