What Went Wrong
Client's WooCommerce store suddenly started returning 500 Internal Server Errors across every page. The site was generating approximately $50,000/month in revenue. The outage began immediately after updating three plugins simultaneously through the WordPress admin dashboard.
The client's hosting support had already tried deactivating plugins manually via FTP but the error persisted. They had no recent backup and their last known good backup was 3 weeks old — unacceptable for an active store with recent orders.
What We Found
Connected via SSH and immediately checked the PHP error log. Found a fatal error: 'Cannot redeclare class WC_Payment_Gateway' in a payment gateway plugin. The plugin update introduced a namespace conflict with another plugin that had hooked into the same WooCommerce payment class.
Dug deeper and found the root cause: Plugin A (payment gateway) updated to use WooCommerce's new abstract class structure, but Plugin B (subscription manager) was still loading the old class definition via a require_once that bypassed WooCommerce's autoloader. The class was being declared twice — fatal error.
Also discovered the hosting company's 'fix' of deactivating plugins via FTP had actually corrupted the active_plugins option in the database by leaving orphaned entries.
How We Fixed It
1. Restored the active_plugins option in wp_options to a clean state using direct MySQL query
2. Activated plugins one by one to isolate the conflict
3. Applied a compatibility patch to Plugin B — added a class_exists() check before the require_once
4. Contacted Plugin B developer with the bug report and patch
5. Set up WP-CLI script for safe future updates: update one plugin at a time, verify site health between each
6. Implemented automated daily backups via server-level cron + off-site storage
Outcome
Site was back online within 47 minutes of initial contact. Zero data loss — no orders, customers, or products affected. The compatibility patch held stable through subsequent updates. Plugin B developer merged the fix into their next release.
Client implemented our recommended update workflow and has had zero downtime incidents in the 6 months since.