What a disastrous deployment: instead of deploying one thing, 50.000 unexpected other things had to be done before. When the "official" deployment was done inside our own network, nothing worked as expected, servers had to be reconfigured, errors everywhere. Mind you it was tested multiple times by multiple people in a testing env. Difference between test and prod, classic.
When it was finally deployed, other errors started emerging, things that weren't considered before came to surface.
On top only the main dev knows the ins-and-outs, no substitute in case anything happens.
Deployment was rolled back in the end.