Denis Ryabov

@writelizwrite Could you check it’s not a conflict with the PageSpeed Ninja plugin? Try to disable PSN plugin and test how website works. I see you use the Ultra settings preset that may conflict with some extensions (in particular, there is an “Optimize integrations (Facebook. Google Plus, etc.)” setting that postpones loading of all JavaScript on the page and rarely results in conflicts with 3rdparty JavaScripts).

The line 138 is related to image rescaling for mobile devices in the “Fixed Ratio” mode (in this mode images are rescale in such a way to have fixed ratio of image width to device screen width on different devices).

It looks like you set “Scale large images” to “Fixed Ratio” and don’t set related “Template width (reference)” parameter.

Anyway, I’d recommend to disable “Scale large images” until the next version will be released, there is a known issue with image rescaling on desktop browsers (a sequence of images in srcset attribute generated by WordPress is sufficient in most cases, and PSN does optimize those images).

If the plugin is uninstalled, first of all try to force page reload in the browser (Ctrl+F5). If it doesn’t work, check that wp-content/advanced-cache.php and wp-content/.htaccess files either don’t exist, or are not related to PSN.

If you use a 3rdparty caching plugin, clear its cache.

Most likely it is Wordfence’s false-positive. *.zz files are used by PSN’s page cache (they contain page content pre-compressed with deflate encoding). To be sure, you can run something like

<?php var_dump(gzinflate(file_get_contents('734dcfb8b0d2d91accebbee525715df3be71d800.zz')));

to check it contains html page sources, but it is very unlikely that someone is trying to store real malware code in PSN’s cache directory.

The problem comes from the following code in your HTML sources (inside of <span class='subtext'>):

<img src="https://das-karrosseri.test-one.dk/wp-content/uploads/2021/04/logo.png" src="" src="" class='alternate' alt='' title='logo' />

Note there are three(!) src tags, and PageSpeed Ninja relies on the last one (dropping others), and so src tag is empty in the optimized page. Most likely the simplest solution is to found where that image tag is generated, and remove duplicated src tags there.

Try to clear Page Cache (see Troubleshooting section in Advanced settings), maybe pages with /s/f.php loader were cached previously.

> After the WP update and update of my theme

Maybe it’s a conflict of above-the-fold CSS rules generated for old theme version and new CSS in the updated theme. Try to regenerate Above-the-fold CSS (or disable it) in Advanced settings (see “Eliminate render-blocking JavaScript and CSS in above-the-fold content” section).

To disable caching of cart, try to add following code to theme’s functions.php file:

if (function_exists('is_cart') && is_cart() && !defined('DONOTCACHEPAGE')) {
    define('DONOTCACHEPAGE', 1);
} 

I can comment the part of error_log file related to PageSpeed Ninja plugin. It looks like you removed that plugin, but the file wp-content/plugins/psn-pagespeed-ninja/public/advanced-cache.php wasn’t removed automatically. Just check this file does exist and remove it manually if necessary (maybe it was just a single request to the site between removing of PageSpeed Ninja files and removing of advanced-cache.php file).

It depends on the level of LaTeX support you need. I’d recommend to use KaTeX (browser-based TeX rendering engine) with auto-render extension (or wrap LaTeX elements into a special div/span nodes, and initialize them “manually”—this way is faster, but auto-render allow to type the text easily).

I know there is a KaTeX plugin for WordPress, try it, most likely it will be quite easy to use (with respect to manual adding javascripts to the page).

Unlikely it’s related to PSN. It looks like your LaTeX codes are not wrapped into Jetpack’s $ latex ...$ block. Could you check the page sources?

I’ve got “MalCare – Pro Firewall
Blocked because of Malicious Activities” message only. Do you have country-based or other restrictions on your website?

Merging of CSS files reduces total size of downloaded data, in this case gzip can use dictionary from previous file instead of re-constructing it from scratch.

Whitespaces should be removed by Standard and libxml HTML parsers (see Advanced settings).

> if you deactivate it, the site becomes unusable

What does “unusable” mean?

> without css styles, and after 0.5 seconds it becomes normal

Looks like incorrect work of the Above-the-fold CSS styles. Current version of the plugin generates Above-the-fold CSS styles for homepage and applies them to other pages, and sometimes it may lead to such an effect (depends on the theme). Try to disable “Above-the-fold CSS” in the “Eliminate render-blocking JavaScript and CSS in above-the-fold content” section of Advanced settings.