The back end of the project is laravel, front end vue, Front and rear end separation project .
A cross domain error occurred when one of the pages was added ,NO 'Access-Control-Allow-Origin';
All other pages on the same system OK, So exclude configuration reasons .
Finally, I found out the problem ：
Back end pages introduce a trait, The trait The name does not match psr-4 Autoload specifications , After changing the name, the error disappears .
does not comply with psr-4 autoloading standard. It will not autoload anymore in Composer v2.0. in phar:///usr/local/bin/composer/src/Composer/Autoload/ClassMapGenerator.php:201