I was not sure if this should go here or under "symfony-bundle"
I had 3 entities with a property name of notes and a formType with $builder->add('notes'); this would cause bin/console translation:extract to fail with the error:
Warning: DOMElement::setAttribute() expects parameter 2 to be string, array given
Renaming the property to note removed this error. I think simply adding a "notes" form element will cause the error. (not tested).
The file is vendor/php-translation/symfony-storage/src/Dumper/Port/SymfonyPort.php line 57