Service providers block artisan optimize every time on composer update - laravel

Question

I pushed some changes to our repo and they auto-deployed to Forge. The deployment failed with this error:
> Illuminate\Foundation\ComposerScripts::postInstall
> php artisan optimize
[Symfony\Component\Debug\Exception\FatalThrowableError]
Class 'MyRepo\MyPackage\MyServiceProvider' not found
Script php artisan optimize handling the post-install-cmd event returned with error code 1
So I edited the config/app.php file to temporarily comment out that service provider line, then re-ran composer update without any problems to artisan optimize this time.
I then uncommented the service provider line and ran artisan optimize again to make sure all was well and got no errors.
Because the composer.lock file changed on Forge after this composer update, I pushed it to the repo.
This triggered yet another artisan optimize error for that same service provider. So I repeated my steps above.
Now every single time there is a new deploy from the repo, artisan optimize triggers that error on that service provider even if we didn't add new service providers.
If I simply run composer update then I'm right back with the same artisan optimize error as before.
Tried doing composer clear-cache but that didn't fix it.
I ran a test script to make sure that service provider is working and autoloaded as expected by calling the class it loads, so I've verified the PSR-4 namespace works just fine.
Here is my project composer.json:
{
"name": "laravel/laravel",
"description": "The Laravel Framework.",
"keywords": [
"framework",
"laravel"
],
"license": "MIT",
"type": "project",
"require": {
"php": ">=7.0.0",
"laravel/framework": "5.2.*",
"laravel/cashier": "~6.0",
"my-repo/my-package": "dev-master"
},
"require-dev": {
"fzaninotto/faker": "~1.6",
"mockery/mockery": "0.9.*",
"phpunit/phpunit": "~5",
"phpunit/phpunit-mock-objects": "3.2.*#dev"
},
"autoload": {
"classmap": [
"database"
],
"psr-4": {
"App\\": "app/"
}
},
"autoload-dev": {
"classmap": [
"tests/TestCase.php"
]
},
"minimum-stability": "dev",
"prefer-stable": true,
"scripts": {
"post-root-package-install": [
"php -r \"copy('.env.example', '.env');\""
],
"post-create-project-cmd": [
"php artisan key:generate"
],
"post-install-cmd": [
"Illuminate\\Foundation\\ComposerScripts::postInstall",
"php artisan optimize"
],
"post-update-cmd": [
"Illuminate\\Foundation\\ComposerScripts::postUpdate",
"php artisan optimize"
]
},
"config": {
"preferred-install": "dist"
},
"repositories": [
{
"type": "git",
"url": "git#bitbucket.org:my-repo/my-package.git"
}
]
}
Here is our private package's composer.json:
{
"name": "my-repo/my-package",
"description": "My package.",
"type": "package",
"require": {
"php": ">=5.5.9",
"illuminate/support": "5.2.*"
},
"require-dev": {
"raveren/kint": "~1"
},
"autoload": {
"psr-4": {
"MyRepo\\MyPackage\\": "src/"
},
"files": [
"src/MyPackage/helpers.php"
]
},
"minimum-stability": "dev",
"prefer-stable": true
}
Even if I change the project's composer.json to pull this by {"type": "path", "url": "./library/my-repo"} I get the same error.
It's as if the optimized class loader is cleared of private repo classes every time I run composer update.
I'm pretty stuck here.