migration process plugin not registering
The module was in a funky state. I ran drush pm-uninstall complimentmigration which gave the following message.


  complimentmigration is already uninstalled.
  There were no extensions that could be uninstalled.


Then I ran drush en complimentmigration which gave the following message.


  The following extensions will be enabled: complimentmigration
  Do you really want to continue? (y/n): y
  Drupal\Core\Config\PreExistingConfigException: Configuration objects (migrate_plus.migration.compliment_xml_to_node) provided by                      complimenttmigration already exist in active configuration in /Users/Sites/devdesktop/drupal8test/core/lib/Drupal/Core/Config/PreExistingConfigException.php:65
  Stack trace:
  0 /Users/Sites/devdesktop/drupal8test/core/lib/Drupal/Core/Config/ConfigInstaller.php(496): Drupal\Core\Config\PreExistingConfigException::create('complimenttmigrat...', Array)
  1 /Users/Sites/devdesktop/drupal8test/core/lib/Drupal/Core/ProxyClass/Config/ConfigInstaller.php(132): Drupal\Core\Config\ConfigInstaller->checkConfigurationToInstall('module', 'complimentmigrat...')
  2 /Users/Sites/devdesktop/drupal8test/core/lib/Drupal/Core/Extension/ModuleInstaller.php(150): Drupal\Core\ProxyClass\Config\ConfigInstaller->checkConfigurationToInstall('module', 'complimenttmigrat...')
  3 /Users/Sites/devdesktop/drupal8test/core/lib/Drupal/Core/ProxyClass/Extension/ModuleInstaller.php(83): Drupal\Core\Extension\ModuleInstaller->install(Array, true)
  4 /Applications/DevDesktop/tools/vendor/drush/drush/commands/core/drupal/environment.inc(131): Drupal\Core\ProxyClass\Extension\ModuleInstaller->install(Array, true)
  5 /Applications/DevDesktop/tools/vendor/drush/drush/commands/core/drupal/environment.inc(198): drush_module_install(Array)
  6 /Applications/DevDesktop/tools/vendor/drush/drush/commands/pm/pm.drush.inc(1180): drush_module_enable(Array)
  7 /Applications/DevDesktop/tools/vendor/drush/drush/includes/command.inc(422): drush_pm_enable('complimentmigrat...')
  8 /Applications/DevDesktop/tools/vendor/drush/drush/includes/command.inc(231): _drush_invoke_hooks(Array, Array)
  9 /Applications/DevDesktop/tools/vendor/drush/drush/includes/command.inc(199): drush_command('complimentmigrat...')
  10 /Applications/DevDesktop/tools/vendor/drush/drush/lib/Drush/Boot/BaseBoot.php(67): drush_dispatch(Array)
  11 /Applications/DevDesktop/tools/vendor/drush/drush/includes/preflight.inc(66): Drush\Boot\BaseBoot->bootstrap_and_dispatch()
  12 /Applications/DevDesktop/tools/vendor/drush/drush/drush.php(12): drush_main()
  13 {main}


I ran drush ev "\Drupal::service('config.manager')-&gt;uninstall('module', 'complimentmigration');", followed by drush en complimentmigration, which gave the following message.


  The following extensions will be enabled: complimentmigration
  Do you really want to continue? (y/n): y
  complimentmigration was enabled successfully.      


This fixed the issue I had.