composer cannot find my installed package - symfony

Question

I have a package in a private github repository.
When I run composer require my_vendor/my_package the package gets added to composer.json and shows up in the vendor directory.
When I run composer remove my_vendor/my_package it gives me a warning:
Package "my_vendor/my_package" listed for update is not installed.
Ignoring.
So when I run composer prohibits my_vendor/my_package it says
Could not find package "my_vendor/my_package" in your project
If I run composer show (after requiring the package) it is not displayed in the list.
This package has a dependency (lexik/authenticationbundle) which is correctly installed, removed and show in list of installed packages (but not listed in the tree view since it is a dependency of a non existent package)...
I have no clue on what could explain this behavior.
Any suggestion?
edit (adding composer.json content)
{
"type": "project",
"license": "proprietary",
"require": {
"php": "^7.1.3",
"ext-ctype": "*",
"ext-iconv": "*",
"api-platform/api-pack": "^1.1",
"composer/composer": "^1.6",
"symfony/console": "^4.1",
"symfony/flex": "^1.0",
"symfony/framework-bundle": "^4.1",
"symfony/lts": "^4#dev",
"symfony/orm-pack": "^1.0",
"symfony/web-server-bundle": "^4.1",
"symfony/yaml": "^4.1"
},
"require-dev": {
"symfony/dotenv": "^4.1"
},
"repositories": [
{
"type": "vcs",
"url": "https://github.com/my_repo/my_package.git"
}
],
"config": {
"preferred-install": {
"*": "dist"
},
"sort-packages": true
},
"autoload": {
"psr-4": {
"App\\": "src/"
}
},
"autoload-dev": {
"psr-4": {
"App\\Tests\\": "tests/"
}
},
"replace": {
"symfony/polyfill-ctype": "*",
"symfony/polyfill-iconv": "*",
"symfony/polyfill-php71": "*",
"symfony/polyfill-php70": "*",
"symfony/polyfill-php56": "*"
},
"scripts": {
"auto-scripts": {
"assets:install %PUBLIC_DIR%": "symfony-cmd",
"cache:clear": "symfony-cmd"
},
"post-install-cmd": [
"#auto-scripts"
],
"post-package-install": [
"App\\Utility\\Bootstrap\\Setup::execute",
"#auto-scripts"
],
"pre-package-uninstall": [
"App\\Utility\\Bootstrap\\Demolish::execute",
"#auto-scripts"
]
},
"conflict": {
"symfony/symfony": "*"
},
"extra": {
"symfony": {
"id": "01C1K60FQVPP7FCAC3YB6639RZ",
"allow-contrib": true
}
}
}
Furthermore, creating a new project and requiring the package correctly adds it to the list of installed packages, thus removing it works fine. Then I tried to delete lock file and running a composer update and eventually I tried to require/remove it but with no luck.

Answer 1

It appears that what was preventing composer to correctly configure required package was a die() in the post-package-install script.
Removing the statement solved the issue.