Mismatched entity and/or field definitions

When trying to use the module the Status report page shows the following:

Mismatched entity and/or field definitions
The following changes were detected in the entity type and field definitions.
Order item

The Quantity field needs to be updated.

Having run into this before I then tried to do a drush entity-updates -y which in turn gave me the following feedback:

commerce_order_item entity type :
The Quantity field needs to be updated.
Do you wish to run all pending updates? (y/n): y
Drupal\Core\Entity\Exception\FieldStorageDefinitionUpdateForbiddenException: The SQL storage cannot change the schema for an existing field (quantity in commerce_order_item entity) with data. in [error]
Drupal\Core\Entity\Sql\SqlContentEntityStorageSchema->updateSharedTableSchema() (line 1597 of
/usr/home/sites/sitename/public_html/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php).
Failed: Drupal\Core\Entity\Exception\FieldStorageDefinitionUpdateForbiddenException: !message in Drupal\Core\Entity\Sql\SqlContentEntityStorageSchema->updateSharedTableSchema() (line 1597 of [error]
/usr/home/sites/sitename/public_html/core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorageSchema.php).
Cache rebuild complete. [ok]
Finished performing updates.

Suggestions?