Sometimes require(vendor/autoload.php) works sometimes it gives error : require(vendor/autoload.php): failed to open stream

Question

I'm using this statement: require './vendor/autoload.php'; in my _aws-config.php file,

after importing that _aws-config, I'm able to add the objects in s3 buckets easily, so no error till now,

but sometimes it gives the following error, when the same _aws-config file is called in some other places :

So why this weird behavior happens? it works at someplace and in some part it don't :(

I had tried several things like

• deleting vendor and composer files and reinstalling them
• running this command: composer dump-autoload
• also tried to run this: composer update --no-scripts

but nothing works :/