I have read that if you enable the plugin "System - cache", the speed of your joomla website increases a lot... I have done it, and it's true, but some navs' css and the Slider dissapears... Do you know why...?
JCH Optimize of one of those plugins that you will have to tinker the settings for.
For me to get it working, I set the following parameters:
- Manage combined files - Combine files in one
- Exclude all extensions - No
Hopefully this will prevent any errors being thrown
No, not unless you share a link to your site or a Codepen with a sample of the code from it.
At the very least you might want to mention the exact version of Joomla you are using, what template you have as the default and what slider extension you are using. We're not mind readers…
From the errors it looks like the vanishing css files are ones that are generated from less or similar preprocessor and cached in the media folder by the extension ("nextend?"). The important part is that the generated cache files have automatically generated unique names that change every time the extension generates them. Which should happen whenever the settings for the extension change. The old version of the cached file is deleted and references to it return now a 404 error.
Now obviously the pages cached by the system plugin do not automatically update to use the new name, and will use the old filename and fail to load them with 404 error. The solution is to purge cache whenever you change the settings and the dynamically generated files change. I think there are extensions that add a clear cache button to the administartor to make this less annoying.