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)…

  • Zak
    • WPMU DEV Initiate

    Yes, I’ve been experiencing the same issue for a few weeks now. Hopefully we can get this escalated because this issue renders Hummingbird useless for my entire network due to the fact that I can’t activate it or it takes down the site with the IDX plugin.

    Appreciate the help.

  • Adam Czajczyk
    • Support Gorilla

    Hello Zak

    I hope you’re well today and I apologize for keeping you waiting. We were testing that and it turns out it’s not actually Hummingbird conflict.

    The “Hummingbird” word in the error log that you shared here is just a path name, not a plugin reference so that might be confusing but Hummingbird is not needed for these error to occur.

    The error is triggered even with no Hummingbird and no other plugins enabled and the default Twenty Seventeen theme active. After registering it’s enough to save settings (even without changing them) on “Optima Express -> IDX Pages” page.

    This would mean that it’s an issue with the Optima Express plugin itself. It might be related to some incompatibility with latest WP or issues with PHP version. However, I recommend reaching out to the Optima Express support and report the bug to them.

    Kind regards,


    • Adam Czajczyk
      • Support Gorilla

      Hello WP Tech

      I just checked the original issue again and while I’m no longer getting that error, I’m getting a lot of deprecation notices. I again tested it on a “clean setup” – with no Hummingbird and other plugins and a Twenty Seventeen theme. Despite that, once I activated Hummingbird, my test site didn’t go down. There was no 500 error, no slow downs or any other issues at all.

      However, I understand that on your site Optima Express is working fine and only enabling Hummingbird causes 500 error. This is a different issue and regardless whether it’s a conflict with Hummingbird or a problem caused by other “under the hood” aspects, we will need to diagnose it separately.

      To let us do this, please start a separate ticket of your own, describing the issue and also make sure that the support access to your site is open, so we could check the site configuration (and test it again on our end using setup similar to yours).

      You can enable support access on “WPMU DEV -> Support” page in your site’s back-end, by clicking on “Grant Support Access” button there.

      Kind regards,


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