WordPress Slow After Update — How to Fix It

WordPress Slow After Update — How to Fix It

You've just updated WordPress, a theme, or a plugin — and suddenly your site is painfully slow. Pages that used to load in one second now take 5-10 seconds. What happened?

It's a scenario I encounter regularly as a WordPress developer. Updates are essential for security, but they can sometimes cause unexpected performance problems.

The good news: it can almost always be fixed. Here's what to do.

Clear All Cache

The first and simplest step. Cached files from before the update can conflict with the new code.

Often this is enough to solve the problem. If not, read on.

Check for Plugin Conflicts

An update can create conflicts with other plugins. The most effective method to find the conflict:

1. Deactivate all plugins except the absolutely necessary ones (caching, security)
2. Test the speed — has it improved?
3. Reactivate one plugin at a time and test after each
4. Identify the problematic plugin — when speed drops again, you've found it

Read more about systematic troubleshooting in my plugin error guide.

Optimise the Database

WordPress updates can leave behind temporary data and unoptimised tables in the database.

• Remove post revisions: WordPress saves all revisions of your posts. Use a plugin like WP-Optimize to clear old revisions.
• Remove transients: Expired transients can pile up. WP-Optimize or Advanced Database Cleaner can remove them.
• Optimise tables: Run a database optimisation via your tool to defragment the tables.

A bloated database is one of the most overlooked causes of slow WordPress performance. Read more in my WordPress speed guide.

Check PHP Version Compatibility

Some plugins aren't compatible with newer PHP versions — or conversely, a PHP upgrade can expose issues in older plugins.

• Log into your hosting control panel
• Check which PHP version you're running
• If you recently upgraded PHP, try going one version down temporarily
• Check the plugin's changelog for known compatibility issues

Check the Error Log

The WordPress error log can reveal exactly what's going wrong. Enable debug logging:

1. Add these lines to wp-config.php:

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);

1. Reproduce the speed problem
2. Check the file wp-content/debug.log for error messages

Look for PHP warnings, deprecated notices, and fatal errors. They often point directly to the problematic plugin or theme.

Roll Back the Update

If nothing else works, you can roll back the problematic update:

• Plugins: Use the WP Rollback plugin to install a previous version
• Themes: Download the previous version from the theme's website and install manually
• WordPress core: It is not recommended to downgrade core — contact a professional instead

When to Get Professional Help

Contact a WordPress developer if:

• You've checked everything above without improvement
• The error log shows complex PHP errors
• Your site is business-critical and you can't afford downtime
• You're unsure about rolling back updates

For more on WordPress speed in general, see my guide to slow WordPress or my overview of the best caching plugins.

Quick Summary

WordPress updates that slow down your site are almost always caused by cache issues, plugin conflicts, or database bloat. Start with the simple fix (clear cache) and work your way systematically to the more complex solutions. And remember: updates are still important for security — don't let a single issue stop you from keeping your site updated.