Today, my co-workers went nuts about the fact their version of our product doesn't work on the pre-production since everything is fine on their local dev machines ^^

After a quick sighting, I figured out what was going on.
There was a package called from non-dev code which was required as a package for development.

The build plan of the application consists of a task which purges dev-packages within the vendor folder, using composer install --no-dev ^^

So the build plan runs perfectly fine, without a single error, but runtime was yelling about a missing class.

It's a delight to be one of the only guys with dev-ops experience in the whole damn building.

xD