Drupal\Component\Plugin\Exception\PluginNotFoundException: The "glossify_taxonomy" plugin does not exist.
There are two approaches (if you don't want to reinstall the module's source code to production and work through the same steps to fully uninstall it).


If you have command line access to the webserver, you could try using drush to uninstall the module on production. Run drush pm-uninstall glossify_taxonomy and then drush pm-uninstall glossify
If that fails, you could schedule a content freeze, download the database to your local instance, and manually set the module as "disabled". Unlike Drupal 7's variables table however, each module does not have it's own row of data.  Instead all module enabled/disabled states are aggregated and saved in the row of data where cid = core.extension within both the config and cache-config tables. To disable the module without fully uninstalling:


load the exported database from prod locally and:
Open ‘config’ table
Search row with ‘core.extension‘
Download Blob object
Unserialize Data (http://www.unserialize.me/ is a quick online tool to serialize and unserialize)
Unset the glossify &amp; glossify_taxonomy modules or remove them from the array.
Serialize Data
Upload Blob object
Save the edited record
Open ‘cache-config’ table and repeat steps 2-8
Export the modified local database
Before making changes on production, keep a backup of the database for quick reversion if needed. 
Import the modified local database back to prod
Test to see if you continue to observe the Missing Module warning/error.