Sorry to not explaining the issue directly in here but let me fix that with this note:

This error can only be achieved via at least 2 classes: a Debugger and a ThrowsDebugInfo class

Debugger.php contains one method which provides debugging info for a given object.

    public static function debug(object $toDebug)
    {
        if (method_exists($toDebug, '__debugInfo')) {
            try {
                $toDebug->__debugInfo();
            } catch (\Exception $e) {
                // Do something
            }
        }
    }

And ThrowsDebugInfo just throws an exception inside the __debugInfo() method.

class ThrowsDebugInfo
{
    public function __debugInfo()
    {
        throw new \Exception('from __debugInfo');
    }
}

The weird part is, that doing a try-catch manually over the ThrowsDebugInfo object does NOT throw an error:

        $obj = new \App\ThrowsDebugInfo();
        try {
            $obj->__debugInfo();
        } catch (\Exception $e) {
            // Do something
        }

but doing basically the same via the Debugger class (which contains a try-catch as well) breaks when xdebug is enabled

        $obj = new \App\ThrowsDebugInfo();
        \App\Debugger::debug($obj);

With the following error:

Warning: Uncaught Exception: from __debugInfo in /Users/kevinpfeifer/Documents/CakePHP/xdebug_test/src/ThrowsDebugInfo.php:10

But ONLY when xdebug is enabled. If I unload the xdebug extension then the second code part also works without a problem.

Xdebug can call __debugInfo at any time, during stack frame stringifcation (happens upon every function call), and at other times. On any object. If you decide to throw an exception in a __debugInfo() method, then this might blow up. It is PHP that generates that error. I don't think there is anything to do here on the Xdebug site, and you should "just" not throw exceptions in __debugInfo() calls.

Seems this was fixed with 3.1.6 as can be seen here: https://bugs.xdebug.org/view.php?id=00002100