Core update installs 8.6.0-beta1 instead of 8.5.6 Using composer I tried to update Drupal 8 to 8.5.6. The update wasn't working, so I changed the dependencies to explicitly require 8.5.6. The update began, but it installed Drupal 8.6.0-beta1. The command I used was composer update drupal/core --with-dependencies -v. 

The updates page still says Drupal 8.5.6 is required. I'm not sure where to go from here.

Should I try to roll it back? I tried requiring Drupal 8.6.0-beta2 and Drupal 8.6.0-rc1, but an error suggested not to update to these versions. I want the site live ASAP, and updated to Drupal 8.5.6.
Solution for me was start from 8.5.0, upgrade to 8.5.5 then run:

composer update drupal/core symfony/* --with-dependencies


I'm now on 8.6.0 ! :)