Critical error in Wordpress navigation menu with PHP 8

[SLH3]

Hi there…
I have the following installation:

• Wordpress 6.4.3
• PHP 8.1.27
• Gantry 5.5.17
• Theme: Helium 5.5.17
  Since the change of PHP 7.4 to PHP 8.1, I have a problem opening the Wordpress navigation menu:
  

The following critical error appears, but is only visible in the backend:

I checked the following:

• Disable various plugins: The error is still persistent
• Downgrade to PHP7.4: Wordpress navigation menu works fine. The PHP-version 8.0, 8.1, 8.2 and 8.3 leads to the critical error.
• Wordpress Query monitor: Doesn’t show an error or a warning for Gantry framework plugin.
• Using the gantry menu editor works fine. But I’m working with the Wordpress menu editor since I have to add blog categories as a menu item.

The frontend works fine. I guess, it’s a Gantry PHP8 compatibility error but I have no idea what it could be😉.

Many thanks and best regards,
David

[SLH3]

Is there anybody else with the same (WordPress) error?

[jazzmang]

Is there anybody else with the same (WordPress) error?

It is working fine on PHP 8.1 on a site we are currently in development.

One thing I can say is that the WP Form and WP SMTP plug-ins in WP do cause issues when working with Gantry, although I don't think the menu was one of them (it was edited under the framework). So my guess is you have a plugin causing an issue. You might try disabling them one by one.

[hexplor]

Can you please show me the list of plugins? I'd love to check what's causing the error...

[SLH3]

Hi there
Sorry for the late reply... I was out of office.

The error was caused by a plugin-in called "Recent Post to WP Nav Menu", which is deprecated for a long time.
Curiously, the plugin wasn't displayed in the plugin list and I didn't deactivate it 3 weeks ago. I found it, by going through the error message step by step (as I should have done it in the first place). After "installing" it again and removing it, everything works!:-)

I would like to thank everybody for their time and efforts! And I'm very sorry I didn't find it in the first place.