Hummingbird Optima Express conflict

When I activated Hummingbird along Optima Express + MarketBoost IDX Plugin it generates a fatal error at the bottom of all front pages.

Fatal error: Uncaught exception ‘Exception’ with message ‘Serialization of ‘SimpleXMLElement’ is not allowed’ in path/to/wp-includes/functions.php:440 Stack trace: #0 path/to/wp-includes/functions.php(440): serialize(Array) #1 path/to/wp-includes/option.php(334): maybe_serialize(Array) #2 path/to/wp-content/plugins/wp-hummingbird/core/modules/minify/class-minify-sources-collector.php(53)…