On several sites I've worked on, for whatever reason before I put my hands on it, the database seems to register a plugin that is no longer in config or code.
This usually goes as follows:
[error] Drupal\Component\Plugin\Exception\PluginNotFoundException: The "name-of-plugin" entity type does not exist. in Drupal\Core\Entity\EntityTypeManager->getDefinition()
In D7, it was relatively straightforward to delete offending module entries from the database. What tables store plugin data so I can tell Drupal to stop looking for them and whitescreening when they can't be found?