Magento – When I use –clear-static-content and after deploy static content doesn’t load any more

I reckon there's several types of errors that can be triggered by the deployment.

First you can see that Exception are handled directly in the execution in Magento/Deploy/Console/Command/DeployStaticContentCommand.php:

    catch (\Exception $e) {
        $output->writeln('<error>' . $e->getMessage() . '</error>>');
        if ($output->getVerbosity() >= OutputInterface::VERBOSITY_VERBOSE) {
            $output->writeln($e->getTraceAsString());
        }
        return;
    }

Regarding the errors that are counted it's a totally different system, you need to look into the Magento/Deploy/Model/Deployer class, the output you got is written by the deploy() method:

$this->output->writeln("\nSuccessful: {$this->count} files; errors: {$this->errorCount}\n---\n");

Now if we check when this errorCount variable is incremented, we find the following in the deployFile() method:

    catch (\Exception $exception) {
        $this->output->write('.');
        $this->verboseLog($exception->getTraceAsString());
        $this->errorCount++;
    }

And as you may have already guessed, the verboseLog() method only outputs when the command is run on verbose mode:

private function verboseLog($message)
{
    if ($this->output->isVerbose()) {
        $this->output->writeln($message);
    }
}

So I reckon you need to run your command like this to see the errors:

php bin/magento setup:static-content:deploy -v

If it doesn't work try the extra verboses:

php bin/magento setup:static-content:deploy -vv
php bin/magento setup:static-content:deploy -vvv

You can use client-side compilation:

1. In the Magento Admin, change the LESS compilation mode to client-side under STORES > Configuration > ADVANCED > Developer > Front-end development workflow > Workflow type. For detailed description see the CSS preprocessing topic.

2. Delete all files in the following directories: pub/static/frontend// var/view_preprocessed/less

Instructions taken from the Dev Docs - http://devdocs.magento.com/guides/v2.0/frontend-dev-guide/css-guide/css_quick_guide_mode.html

Although I recommend using your own Gulp/Grunt setup over the build-in ones but that's a larger task than one admin setting.