I received the following error when the scaffold was trying to download "initial" files during composer install, but they already exist and there are no curl requests to make.

Script DrupalComposer\DrupalScaffold\Plugin::scaffold handling the drupal-scaffold event terminated with an exception
[ErrorException]                                                            
  count(): Parameter must be an array or an object that implements Countable

This solves the problem by avoiding "curling" when there's nothing to curl.
The actual error is because curl never gets set up correctly and then when it gets to the do while in fetchWithPrestissimo(), $multi->remain() returns NULL (because it was never initialised).