Hello

The tag system appears to be working normally on all other pages and when adding images and making new tags for them, or assigning tags and showing tag collections.
But when opening the admin backend tag manager (Photos -> Tags) The page won't load at all, just throwing a PHP error:

Fatal error: Uncaught TypeError: Argument 3 passed to Smarty_Internal_Runtime_FilterHandler::runFilter() must be an instance of Smarty_Internal_Template, null given, called in /home/******/public_html/gallery/piwigo-2.0.6/include/smarty/libs/sysplugins/smarty_internal_templatecompilerbase.php on line 429 and defined in /home/******/public_html/gallery/piwigo-2.0.6/include/smarty/libs/sysplugins/smarty_internal_runtime_filterhandler.php:33 Stack trace: #0 /home/******/public_html/gallery/piwigo-2.0.6/include/smarty/libs/sysplugins/smarty_internal_templatecompilerbase.php(429): Smarty_Internal_Runtime_FilterHandler->runFilter('post', '<?php\n/* smarty...', NULL) #1 /home/******/public_html/gallery/piwigo-2.0.6/include/smarty/libs/sysplugins/smarty_internal_templatecompilerbase.php(330): Smarty_Internal_TemplateCompilerBase->postFilter('<?php\n/* smarty...') #2 /home/******/public_html/gallery/piwigo-2.0.6/include/smarty/libs/sysplugins/smarty_template_compiled.php(236): Smarty_Internal_TemplateCompilerBase->compil in /home/******/public_html/gallery/piwigo-2.0.6/include/smarty/libs/sysplugins/smarty_internal_runtime_filterhandler.php on line 33

(yes I know the paths say 2.0.6 but it's just a foldername where the gallery was originally installed. It's always been there through several upgrades.)

I just yesterday upgraded Piwigo from 11.3 I think. It was an 11 branch in any case. And never noticed the error before now.
I have had some problems with a virtual gallery with the same name as a folder gallery, So i had a duplicate gallery. There was no way of moving the images to the virtual gallery, they stayed in the folder version no matter what I did. So I eventually removed the gallery folder and re-synced the galleries. Then re-uploaded a few images. That seemed to work fine.
But I suspect something may have happend with the tags at that point. That's all I can think of.

I upgraded via the automated updated in the site. But tried downloading the full intstall folder and replacing the smarty_internal_runtime_filterhandler.php file with a clean copy from the full install download. But it makes no difference. The root of the problem doesn't seem to be the smarty_internal_runtime_filterhandler.php file itself. Maybe some corruption in the database?

I've also tried other browsers. Cleared the browser cache.

and:
    Update albums' information
    Update photos' information
    Repair and optimize database
    Reinitialize integrity check
    Purge user cache
    Delete orphan tags
    Purge sessions
    Purge compiled templates

Now I'm at a loss.

The gallery works fine otherwise. But if anyone can help me figure out what's broken, it would be appreciated.

    Piwigo 11.4.0 Check for upgrade
    Operating system: Linux
    PHP: 7.3.27 (Show info) [2021-04-25 14:20:34]
    MySQL: 5.7.34 [2021-04-25 14:20:34]
    Graphics Library: External ImageMagick 6.9.10-68