Finally I've found a solution. It was a deployment issue with my particular setup, but it could help others in similar situations.
To shorten: rebuild your bootstrap.php
with
php vendor/sensio/distribution-bundle/Sensio/Bundle/DistributionBundle/Resources/bin/build_bootstrap.php
If for any reason you are forced to run composer
updates in Production
with the --no-scripts
option (as I am due to shared hosting restrictions), forgetting to rebuild that file can cause this issue.