Wp-Admin broken due to plugin

We have the latest version of everything.

Your plugin runs the following…

admin_init() (wp hook)
_create_db_structure()
which tries to execute a DROP INDEX purchase_id
Which fails, causing a blank white page for wp-admin dashboard.

I had to modify your plugin to make it work:

$sql= "SHOW INDEX FROM '.$wpdb->prefix.SDDB_PURCHASE.' WHERE KEY_NAME = 'purchase_id'";
if ($wpdb->query($sql)) {
	$results=$wpdb->get_results($sql);
	if ($wpdb->num_rows > 0) {
		$sql = "ALTER TABLE ".$wpdb->prefix.SDDB_PURCHASE." DROP INDEX purchase_id";
		$wpdb->query($sql);
	}

}

Please fix this, so that we can resume updating your plugin.
Or explain to me why this is happening, is there something wrong?
Thank you!

https://wordpress.org/plugins/sell-downloads/