Drupal 8 Custom Migration
There are several things to check for when troubleshooting migrate/migrate plus. 

Based on "not registering" make sure you set id: my_migration instead of id: beer_term or it won't show up when you run drush ms. That's the easy one, hopefully it's that. If not...

Failures resulting from errors in your migration configs will be silent most of the time. When they're not silent, they tend to send you on a wild goose chase for something pretty unrelated to what failed. This can make it frustrating to pinpoint what went wrong. Quadruple check your .yml syntax.

Secondly, make sure your config (.yml) files are named correctly. They should be named and placed exactly like /drupal/modules/custom/my_module/config/install/migrate_plus.migration.my_migration.yml The config files should NOT be named my_module.migration.my_migration.yml. As @mike ryan points out, resist the temptation to do so.

If you've done all of the above after uninstalling and reinstalling your module, your migration should show up when you do a migrate status check.