Debugging ui components

What I found so far is that when rendering the layout this stack is followed.

• \Magento\Framework\View\Layout::generateElements
• \Magento\Framework\View\Layout\GeneratorPool::process

Now, depending on the type of the layout a different layout generator is called in

foreach ($this->generators as $generator) {
    $generator->process($readerContext, $generatorContext);
}

For the Ui components ... continuing the stack:

• \Magento\Framework\View\Layout\Generator\UiComponent::process()
• \Magento\Framework\View\Layout\Generator\UiComponent::generateComponent()
• \Magento\Framework\View\Element\UiComponentFactory::create()
• \Magento\Ui\Model\Manager::prepareData()
• \Magento\Ui\Model\Manager::evaluateComponents()
• Magento\Framework\Data\Argument\InterpreterInterface::evaluate.

Here again it depends on the argument type that needs to be interpreted.
You can find some interpreters here lib/internal/Magento/Framework/Data/Argument/Interpreter/

This is as far as I got.
I know it's not a full explanation, but these are some points where you can identify if something is wrong with your ui component.