Fatal error “Liip\TestFixturesBundle\Test\FixturesTrait” not found while loading

[tacester]

Installed on a freshly upgraded Matic 4.4.10 to 5.0.3 instance using composer and ran into the following fatal error...

php.CRITICAL: Fatal Error: During class fetch: Uncaught ReflectionException: Class “Liip\TestFixturesBundle\Test\FixturesTrait” not found while loading “MauticPlugin\SparkpostBundle\Tests\Functional\EventSubscriber\CallbackSubscriberTest”.

I was able to overcome the error by running composer install --no-dev --optimize-autoloader

I left a post on the Mautic forum here