Unsupported operand types: string * int

Hello,

I recently recognized our image galleries do not work any longer (no idea since when). On frontend we face a “critical error” when opening a gallery, while log says:

AH01071: Got error 'PHP message: PHP Warning: Attempt to read property "ID" on null in /var/www/vhosts/*************/wp-includes/link-template.php on line 394; PHP message: PHP Warning: Attempt to read property "ID" on null in /var/www/vhosts/*************/wp-includes/link-template.php on line 409; PHP message: PHP Warning: Attempt to read property "ID" on null in /var/www/vhosts/*************/wp-includes/link-template.php on line 394; PHP message: PHP Warning: Attempt to read property "ID" on null in /var/www/vhosts/*************/wp-includes/link-template.php on line 409; PHP message: PHP Fatal error: Uncaught TypeError: Unsupported operand types: string * int in /var/www/vhosts/*************/wp-content/plugins/nextgen-gallery/src/DisplayTypes/Thumbnails.php:72\nStack trace:\n#0 /var/www/vhosts/*************/wp-content/plugins/nextgen-gallery/src/DisplayedGallery/Renderer.php(417): Imagely\\NGG\\DisplayTypes\\Thumbnails->index_action()\n#1 /var/www/vhosts/*************/wp-content/plugins/nextgen-gallery/src/DisplayedGallery/Renderer.php(247): Imagely\\NGG\\DisplayedGallery\\Renderer->render()\n#2 /var/www/vhosts/*************/wp-content/plugins/nextgen-gallery/src/DisplayTypes/Albums/SharedController.php(647): Imagely\\NGG\\DisplayedGallery\\Renderer->display_images()\n#3 /var/www/vhosts/*************/wp-content/plugins/nextgen-gallery/src/DisplayedGallery/Renderer.php(417): Imagely\\NGG\\DisplayTypes\\Albums\\SharedController->index_action()\n#4 /var/www/vhosts/*************...', referer: https://*************/galerie/interne-galerie/

Plugins, WordPress are current, caching-plugin was deactivated, but with no use. Someone can help?

Thanks & kind regards,

Norman

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