Unable to update drupal 8.4.3 to 8.4.5 using composer - drupal-8

Question

I'm following this guide to "Update core via Composer" and I have my backups. The document says to run
composer update drupal/core --with-dependencies
When I do, I get:
Loading composer repositories with package information
Updating dependencies (including require-dev)
Nothing to install or update
Generating autoload files
> Drupal\Core\Composer\Composer::preAutoloadDump
> Drupal\Core\Composer\Composer::ensureHtaccess
drush core-status says I'm on version 8.4.3, so I expected the composer update command to move me to 8.4.5.
Later the document says to "Review the status report page for errors" and the only error listed is that I need to be on version 8.4.5
There must be something missing from the update documentation, and I can't figure out what it is.
Edit: Thanks Robb Davis, I tried:
rm -rf vendor
rm composer.lock
composer update drupal/core --with-dependencies
That gave me no change -- leaving me with an 8.4.3 installation.
I tried composer require drupal/core:8.5 which gave me:
$ composer require drupal/core:8.5
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.
Problem 1
- Installation request for drupal/drupal dev-master -> satisfiable by drupal/drupal[dev-master].
- don't install drupal/core 8.5.0|remove drupal/drupal dev-master
- Installation request for drupal/core 8.5 -> satisfiable by drupal/core[8.5.0].
Installation failed, reverting ./composer.json to its original content.
Nothing in that message makes any sense to me. So I'm still lost.

Answer 1

I was trying to update 8.5 to 8.6. Dumping the core and vendor folders in addition to the composer.lock file did not work for me.
I was able to resolve this issue by removing the core/composer.json line from the merge-plugin include array and running composer update drupal/core --with-dependencies.
My merge-plugin key in the composer.json file in the docroot looks like:
"merge-plugin": {
"include": [],
"recurse": true,
"replace": false,
"merge-extra": false
}

Answer 2

yes this is kind of foobar. There is a blog post about it here:
https://orkjern.com/updating-to-drupal-85-with-composer
The solution in the blog didn't work for me but a solution in the comments did:
Delete your vendors directory
Delete your .lock file
Run composer update drupal/core --with-dependencies
This will rebuild / redownload everything but it seems to work and updates properly to 8.5 (the most recent stable version of core).