LOTS of 500 Internal Server Errors And Content Decoding Failed Errors

Hello,

On a WP 4.5.3 multisite network of 60 sites, we recently began experiencing a LOT of 500 Internal Server Errors, especially when editing posts and pages.

The errors can be seen in the Browser console and they all reference:

POST http://soobahkdo.biz/wp-admin/admin-ajax.php 500 (Internal Server Error)

Each 500 error may have additional references listed for different plugins, wordpress functions, etc., etc.

Near the same time we also began experiencing quite a few of these errors:

POST http://soobahkdo.biz/wp-admin/admin-ajax.php net::ERR_CONTENT_DECODING_FAILED

I am not sure how to interpret what the console errors are telling me.

In the admin area the browser console errors are very evident when pages are loading or features are used.

I have tried most of the traditional troubleshooting techniques like eliminating plugins, etc without success.

Editing posts and pages and other things work ok part of the time and hang up at other times. Selecting media for insertion may fail and inserting images in the post editor window may fail intermittently and setting the featured image may fail intermittently. When those failures occur there are multiple 500 Server Errors in the console and/or Content Decoding Failed Errors. Sometime refreshing the page will resolve the issue for a while.

Past experience with some similar erratic behavior like this was ultimately found to be caused by a javascript conflict, but I need assistance in that realm.

Please DO NOT suggest upgrading to 4.6 right now. We probably will within a month, but we need to allow time for all the plugin and theme crews to catch up before we make that change.

Any assistance will be appreciated.

  • Adam Czajczyk

    Hello SooBahkDo,

    I hope you're fine today and thank you for your questions!

    As for Internal server error 500.

    It's a general and not precisely defined error but in case of WordPress it's in most cases caused by insufficient memory resources. I'm not sure how much memory is assigned/allowed for PHP scripts on your server but if you got WP DEV Dashboard plugin enabled you can easily find that out. To do this please go to the "WPMU DEV -> Support" page and click on "System Info" button. The first tab will show you (in "memory_limit" line) an amount of memory made available to PHP.

    Once you found that out, please add following line to the "wp-config.php" file of your site:

    define('WP_MEMORY_LIMIT','256M');

    where 256M should be replaced with aforementioned value. The line should be located above the "/*That's all, stop editing!*/" line.

    Make also sure that your storage/disk space quota on a server isn't hitting limits as it may cause such an unexpected behavior as well.

    As for "net::ERR_CONTENT_DECODING_FAILED" error.

    This is most likely caused by an attempt of delivering gzip compressed content to the browser while the content in fact is not gzipped. In other words, HTTP headers suggest to the browser that the response is in gzip format but in fact the response goes in an uncompressed/plain form.

    Most likely the reason for this is that server is not able to deliver gzipped content but gzip compression is "forced" on some level. I'm not able to tell you how this happens without checking the site first but I'd start with checking plugins and if there's gzip compression enabled enywhere, I"d try disabling it.

    The XSS Auditor refused to execute a script in 'http://soobahkdo.biz/wp-admin/post.php' because its source code was found within the request. The auditor was enabled as the server sent neither an 'X-XSS-Protection' nor 'Content-Security-Policy' header.

    I would suspect that this is a result of those other two issues. It seems that the /wp-admin/post.php script is being delivered to user browser instead of being executed on a server or some associated JavaScripts are malformed. This is causing XSS Auditor (which is a part of Chrome browser built-in security suite) to block such a script in order to protect user. XSS stands for "Cross Site Scripting" which is quite a popular way to inject malicious scripts into websites, user browsers etc. I think it would be critical to deal with 500 Internal Server Error first and the content decoding fail error first and then see if this also fixed that issue.

    Best regards,
    Adam

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