Complete website crash after upgrading from an old version (

We are about to update our site from a rather old version of BeTheme ( but it makes the site completely unavailable.

On the WP update core page everything seems to go just fine during the update process, we got a success message. But then when refreshing the site it is not available.

The recovery email that WP sends out shows the following info (some parts are in Hungarian but you should see the error):

A(z) /data/www/html/wp-content/themes/betheme/functions/builder/pre-built/class-mfn-pre-built-sections-api.php fájl 14 sora egy E_ERROR típusú hibát okoz. Hibaüzenet: Uncaught Error: Class “Mfn_API” not found in /data/www/html/wp-content/themes/betheme/functions/builder/pre-built/class-mfn-pre-built-sections-api.php:14

Stack trace:

#0 /data/www/html/wp-content/themes/betheme/functions/builder/class-mfn-builder.php(43): require_once()

#1 /data/www/html/wp-content/themes/betheme/functions/builder/class-mfn-builder.php(63): Mfn_Builder->__construct()

#2 /data/www/html/wp-content/themes/betheme-child/functions.php(192): require_once(‘…’)

#3 /data/www/html/wp-settings.php(525): include(‘…’)

#4 /data/www/html/wp-config.php(101): require_once(‘…’)

#5 /data/www/html/wp-load.php(37): require_once(‘…’)

#6 /data/www/html/wp-admin/admin.php(34): require_once(‘…’)

#7 /data/www/html/wp-admin/index.php(10): require_once(‘…’)

#8 {main}


Our IT was able to get another view on this fatal error (attached as image)

The system details are shown in the following screenshots (taken before the update attempt):

More detailed system info:

### Begin System Info ###



PHPMailer Version       6.2.0

Permalink Structure      /%postname%/

PHP Version          8.0.27

MySQL Version         10.5.13

Web Server Info        nginx/1.14.1

User Agent          Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0

Multi-site          No

PHP Memory Limit       512M

PHP Post Max Size       64M

PHP Upload Max File size   64M

PHP Time Limit        1800 sec

PHP Max Input Vars      5000

WP_DEBUG           Disabled


WP Table Prefix        Length: 3 Status: Acceptable

WP DB Charset/Collate     DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_520_ci

WP ID             OK

Session            Disabled

Session Name         PHPSESSID

Cookie Path          /

Save Path           /var/lib/php/session

Use Cookies          On

Use Only Cookies       On

WordPress Memory Limit    512 MB

WordPress Upload Size     1 GB

Filesystem Method       direct

SSL SUPPORT          SSL extension loaded

MB String           MB String extensions loaded

CURRENT THEME                Betheme Child:

Please help me straightening this out.


  • Hi,

    I can see that you have a child theme active.

    Please switch to the parent theme and check if the problem persists.

    You can also disable all the plugins to see if none interfere with it.

    Best regards

  • Hi,

    We switched to the parent theme and the update was successful, the site stayed working, but obviously looked awkward. Switching back then to the child theme we got fatal error again:

     Fatal error: Uncaught Error: Class "Mfn_API" not found

    in /data/www/html/wp-content/themes/betheme/functions/builder/pre-built/class-mfn-pre-built-sections-api.php on line 14

    Call stack:

    1. require_once()
    2. wp-content/themes/betheme/functions/builder/class-mfn-builder.php:43
    3. Mfn_Builder::__construct()
    4. wp-content/themes/betheme/functions/builder/class-mfn-builder.php:63
    5. require_once()
    6. wp-content/themes/betheme-child/functions.php:192
    7. include()
    8. wp-settings.php:525
    9. require_once()
    10. wp-config.php:97
    11. require_once()
    12. wp-load.php:37
    13. require_once()
    14. wp-admin/admin.php:34
    15. require_once()
    16. wp-admin/themes.php:10

    What is the solution here to have an updated theme but keep the design changes we made throughout the years without having to redo them all again?


  • You have to revive which changes in the child theme cause this. If you do not know how to do this, you should contact your web developer, as support does not cover child theme modifications.

    Best regards

  • edited September 2023

    Dear Phil,

    Thank you. We have no other choice than keeping the current version ( as rewriting all the custom design modification would not be cost effective.

    We bumped into another problem when upgrading the WP version. On 5.6.3 everything works fine, but on the latest version (6.3.1) we got a 502 bad gateway error when trying to open any of the pages for editing.

    We turned off all the plugins and turned them back one-by-one. We noticed that this error occurs when we switch back the Ultimate Member plugin (latest version 2.6.10).

    The error is present even if we change back to the standard theme from the child theme.

    In the error log we found the following entry (repeated about 20 times in a row):

    "2023/09/05 15:03:11 [error] 1118#0: *2531 FastCGI sent in stderr: "s/betheme/functions/builder/class-mfn-builder-admin.php on line 458PHP message:  PHP Warning: Trying to access array offset on value of type bool in /data/www/html/wp-content/themes/betheme/functions/builder/class-mfn-builder-admin.php on line 458PHP"

    Line 458 in class-mfn-builder-admin.php looks like this:

    Please help us out here.


  • You can add !empty for 1st $item['size'] variable, like:

    !empty['size'] ?

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