Preloading of critical assets is a premium feature of WP-Optimize.
Some assets which are considered critical might be loaded later because they are included via a script or from within a CSS file.
A typical example are font files, background images, or scripts which are loaded from an other scripts. They will typically start loading once the other assets have been downloaded and parsed.
Preloading those assets will enable them to be loaded in priority, and could result in a faster page load.
You can check Google’s articles here and here for more technical informations.
This usually means one or more of your CSS files are incompatible with the minification or merging process. It can also be caused by errors in the CSS’s syntax.
You can check the CSS’s syntax by using an online CSS syntax checker such as csslint.net.
If your syntax is not causing the issue, or you cannot change the file with an issue, you can either
- exclude the problematic CSS files from the minification and merging process.
- or not merge the CSS.
To exclude individual CSS files from the minification and merging process, you can go to WP-Optimize > Minify > CSS and go to the “Exclude the following CSS files from processing” section (for more precise steps on how to exclude your CSS files go here).
To disable merging of CSS files, follow the instructions here.
You can defer your CSS files by going to WP-Optimize > Minify > CSS and going to the “Load the following CSS files asynchronously” section.
For more precise steps on how to defer your CSS files go here.
You can merge your CSS files without minifying them — or vice-versa — by doing the following:
- Go to WP-Optimize > Minify > CSS
- Scroll to the “CSS options” section
- Uncheck the “Enable minification of CSS files” or “Enable merging of CSS files” checkbox, depending on your needs:
- Click ‘Save settings’