When a feature stops working, a layout breaks or the editor will not load, the cause is usually two plugins (or a plugin and the theme) that do not get along. A systematic test finds the culprit in minutes instead of hours.
Before you start
- Write down exactly how to reproduce the problem, for example "clicking Add to cart on any product does nothing".
- Take a backup, or work on a staging copy.
- Purge LiteSpeed Cache and test in a private window so you are not looking at a cached page.
Check the obvious first
- Did the problem start right after an update or a new plugin? Start with that plugin.
- Look at the PHP error log (
error_login the site folder, or cPanel → Metrics → Errors). - Open the browser console (F12 → Console). JavaScript errors often name the plugin's script file.
Use Health Check troubleshooting mode
The Health Check & Troubleshooting plugin lets you disable plugins only for your own session, so visitors are not affected.
- Install and activate Health Check & Troubleshooting.
- Go to Tools → Site Health → Troubleshooting and click Enable Troubleshooting Mode.
- You now see the site with all plugins disabled and a default theme. Check whether the problem is gone.
- Use the Troubleshooting Mode menu in the admin bar to enable plugins one by one, testing after each.
- When the problem returns, the plugin you just enabled is involved.
- Click Disable Troubleshooting Mode when finished.
The half-split method
With many plugins, test in halves instead of one by one:
- Deactivate half of the plugins and test.
- If the problem is gone, the culprit is in the deactivated half; otherwise it is in the active half.
- Split the suspect group again and repeat until one plugin is left.
Twenty plugins take about five rounds this way. On a live site, do this on staging, or use the bulk actions in Plugins → Installed Plugins during a quiet period.
When the dashboard is unreachable
Rename wp-content/plugins in cPanel → File Manager to disable all plugins at once, or with WP-CLI run wp plugin deactivate --all, then reactivate in groups.
Check the theme
If the problem remains with every plugin off, switch to a default theme. If that fixes it, the theme or a child theme customisation is at fault.
Fix the conflict
- Update both plugins; many conflicts are fixed in later versions.
- Check the plugin's support forum on wordpress.org for the same report.
- Look for duplicated functions: two caching plugins, two SEO plugins or two form plugins loading the same library.
- Exclude the plugin's scripts from LiteSpeed Cache minify and combine.
- Replace the plugin with an alternative if the developer does not respond.
Report it well
When you contact a plugin developer, include the steps to reproduce, the error message, your WordPress and PHP versions (Tools → Site Health → Info) and the name of the conflicting plugin.