How do I troubleshoot 403, 500, 502, 504, 524 Server Errors During Scans?

The WP ADA Compliance plugin inspects every link and file on the installed website. This process takes time and can use a lot of server resources. While the plugin is designed to mitigate common issues such as PHP settings that limit execution time and memory usage sometimes this may not be enough. If you notice 502, 504 or 500 server errors in your log files, in the browser Javascript Console or on the error screen we suggest the following:

502 / 504 / 524 Errors

These errors normally occur while scanning pages with a large number of links and indicate that the server timed out before a scan cycle has completed. If you see these server errors, increase the PHP max_execution_time to at least 300 and memory_limit to 256MB or 700MB for PDF scans. It may be necessary to increase the max_execution_time and memory_limit even further if errors persist. Other potential solutions include:

1. Hide the error summary while the scan is running. When the error summary is hidden it will not refresh after each scan cycle and use less server resources.
2. Disable link scans which are only necessary if you have a lot of content that was created outside of WordPress.
3. Enable cron scans under “Scan & Notification” settings and if not already done, setup a cron job in your control panel. A variety of frequencies are provided to complete the scan in a timely manner.
4. On the settings page, under “Scan & Notification” settings:  Lower the number of posts to scan each cycle.

500 Errors

The deep scan process can us a lot of server resources when conducted from the report screen and on many budget friendly hosting packages server resources are severely throttled. If this occurs you will see 500 server errors displayed in your browser.

To verify that this has occurred, check your host’s resource usage statistics or contact your host to see if your account was limited during the affected time period. If available, access cPanel and under Metrics go to CPU and Concurrent Connection usage. This will show any recent faults. You may also be able to watch the CPU usage as you are scanning on the right side of the cPanel screen, under “Statistics”.

In order to successfully run a scan you will need to lower resource usage.

Potential solutions include:

1. Hide the error summary while the scan is running. When the error summary is hidden it will not refresh after each scan cycle and use less server resources.
2. Disable link scans which are only necessary if you have a lot of content that was created outside of WordPress.
3. Enable cron scans under “Scan & Notification” settings and if not already done, setup a cron job in your control panel. A variety of frequencies are provided to complete the scan in a timely manner.
4. On the settings page, under “Scan & Notification” settings:  Lower the number of posts to scan each cycle.
5. Disable the incorrect white space rule which tends to use a lot of resources.

403 Errors

403 errors indicate that something is blocking the scan process. This could be a server side firewall or a WordPress security plugin. Review firewall block logs and add whitelist entries if required or disable  security plugins during the scan process.

Related article: Troubleshooting issues with slow and long scans on large website?