WordPress cache plugins can cause all sorts of problems due to misconfiguration or conflicts. As with any other plugin, it is important you set your cache plugin correctly, and test everything to make sure everything is fine.
Cache plugins can cause problems on server side and in the browser.
Server side issues
Cache plugins can cause server side issue in rare instances. Most problems on the server side are caused by using two types of cache: object cache and database cache. These two cache methods are trying to optimize calls to database and they are caching results from database queries. So, if a plugin makes a request to get some data, cache plugin will first try to return cached data if previously cached. This can lead to plugins getting old or wrong data, especially if the website is dynamic and deals with multiple users, time sensitive information or things like that.
Most problems related to cache plugins can be solved by disabling database and object caching methods. Before asking for any support, make sure that you don’t have these cache methods active. If you use these cache methods, it is high probability that we can’t help you until you disable both these methods because they can provide you with false or old data. Plugins that support such cache methods are W3 Total Cache and WP Super Cache. Common problems caused by these cache methods are:
- You change some plugin settings and save changes, but once the page loads again, you again see old settings.
- You get errors about missing methods from incomplete objects, and this is direct result of object cache.
- After plugin update, you start getting errors or whole website goes blank, this can be caused by database and object cache methods.
Client side issues
Most cache plugins have minification features. This will merge mulitple JavaScript files into one file, and perform compression and minification to make this resulting JavaScript file smaller. But, this will work fine only if all JavaScript files are valid. If any JavaScript file minified this way has syntax errors (missing semi-colons), it will break the whole minified file and JavaScript execution in browser will fail and break the page.
To solve this you need to test for JavaScript errors in browsers to determine where the problem is. This is not easy thing to fix, and usually you need to disable minification in cache plugin, or to fix the issues in JavaScript files causing problems.
