$ composer create-project drupal-composer/drupal-project:7.x-dev \
example --stability dev --no-interaction
This will copy the drupal-project to the example directory, and download Drupal core and some handy packages. This is a good point to cd into the example directory, run git init , and to then create your initial commit for your project.
Wow! For me it was the inclusion of the settings.local.php file which wasn't working anymore locally.
Previously I did it like so, and still do on the live server where it's still working. But locally on my macOS with MAMP this returned a wrong path and so the settings.local.php file wasn't included anymore and Drush didn't found the default site anymore.
I ran into the same issue. My issue was related to upgrading to a new Drupal core minor version (ex: 8.6 to 8.7). If that's not the case for you, then my steps may be unnecessary.
I was able to resolve it by removing the core directory of Drupal. Then run composer update drupal/core --with-dependencies. I believe the issue stems from the core/composer.lock ...