Since other attribute types show on screen, but the classic dropdown doesn't, this seems to confirm my suspicions of a few keys being removed from the database which well... doesn't happen as much now-a-days and is reversed by installation of ZC 1.5.5 and/or running the install of this plugin.

Doing so will/should execute the query(ies) below to restore the missing attribute types (any existing variants will remain untouched, but for now the SBA configuration settings will get reset to "factory default", then after the install, you will want to change the option name type to the added SBA basic/simple dropdown to get the desired results:
Code:
UPDATE configuration set configuration_group_id = 6 where configuration_key in 
	('PRODUCTS_OPTIONS_TYPE_SELECT', 'UPLOAD_PREFIX', 'TEXT_PREFIX');
	INSERT IGNORE INTO configuration (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, last_modified, date_added, use_function, set_function) VALUES ('Product option type Select', 'PRODUCTS_OPTIONS_TYPE_SELECT', '0', 'The number representing the Select type of product option.', 6, NULL, now(), now(), NULL, NULL);

	INSERT IGNORE INTO configuration (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, last_modified, date_added, use_function, set_function) VALUES ('Upload prefix', 'UPLOAD_PREFIX', 'upload_', 'Prefix used to differentiate between upload options and other options', 6, NULL, now(), now(), NULL, NULL);
	INSERT IGNORE INTO configuration (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, last_modified, date_added, use_function, set_function) VALUES ('Text prefix', 'TEXT_PREFIX', 'txt_', 'Prefix used to differentiate between text option values and other option values', 6, NULL, now(), now(), NULL, NULL);