If you’re running a WooCommerce store, ensuring that your checkout page functions perfectly is crucial. A failed checkout page not only aggravates users but directly affects your revenue. This is a situation one WordPress site owner faced when using both SG Optimizer and WP Super Cache plugins on their site. What initially seemed like an ideal optimization stack quickly became a troubleshooting nightmare.

TL;DR

Using SG Optimizer and WP Super Cache together led to catastrophic caching of the WooCommerce checkout page, causing failed transactions and user frustration. The two plugins conflicted in how they handled dynamic content, particularly pages like the cart and checkout which should never be statically cached. The debugging process revealed overlapping caching rules, duplicate optimization efforts, and a surprisingly simple solution. If you’re using two optimization plugins, make sure their functions don’t overlap in critical areas like session-based pages.

Initial Symptoms and the First Red Flag

Users first started reporting strange checkout behaviors: cart items would disappear mid-session, orders wouldn’t go through, and the spinner on the checkout button kept spinning endlessly without any confirmation. Naturally, the site owner first suspected typical issues like:

• Plugin conflicts
• Payment gateway errors
• SSL misconfigurations

However, none of these checks revealed the true culprit. Error logs were clean. Browser console logs showed no JavaScript errors. Yet, the checkout page kept failing to submit orders correctly.

Realizing the Dual Cache Overlap

Both SG Optimizer and WP Super Cache are powerful in their own right. SG Optimizer, built by SiteGround, offers a suite of optimizations tailored for their hosting platform, while WP Super Cache provides static caching to boost loading speeds. It wasn’t obvious at first, but having both can be redundant and even harmful.

Upon closer inspection, the site owner realized that:

• SG Optimizer was already handling page caching at the server level
• WP Super Cache was also generating static HTML versions of pages, including dynamic ones
• The checkout page had been cached unintentionally, stripping away its dynamic content

The checkout page stopped working because static caching doesn’t allow for dynamic interactions required by WooCommerce’s session-based cart system. Once the checkout page is cached as a static page, every user gets served the same HTML, rendering individual sessions useless.

The Step-by-Step Debugging Process

1. Identifying Disruption in Functionality

The first step in debugging was isolating the malfunction. Since the home, shop, and even cart pages worked fine, attention turned toward the checkout flow. A WooCommerce plugin conflict test (disabling all non-essential plugins) revealed that the problem persisted only when both optimization plugins were active.

2. Reviewing Caching Behavior

Next, the site owner reviewed caching rules:

• SG Optimizer excluded checkout and cart pages by default
• WP Super Cache, however, did not exclude them automatically unless manually configured

This led to the discovery of cached /checkout and /cart pages sitting in the wp-content/cache folder. A quick purge of cache followed by testing led to temporary restoration of checkout functionality, confirming the source of the issue.

3. Reviewing .htaccess Rules

Next came the exploration into the .htaccess file. There were rules being injected by both plugins, leading to:

• Redundant gzip compression (could slow down performance)
• Overlapping expiration headers
• Conflicting cache-control headers

These had to be manually compared and cleaned to remove anything that was clashing or redundant. The key takeaway? Don’t let two optimization plugins write to your .htaccess file at the same time without careful review.

4. Testing in Incognito Mode

Still unsure whether the problem was browser-related, testing in incognito mode and across browsers proved consistent behavior. Sessions failed when both plugins were on, and succeeded when either one was disabled — clearly isolating the root cause.

5. Choosing Which Plugin to Keep

Given the redundancy and conflict-prone setup, the final decision was to retain only one plugin. Since SG Optimizer is tightly integrated with the hosting platform, it was the more logical plugin to keep. WP Super Cache was completely disabled and deleted.

Post-removal of WP Super Cache, the checkout process worked perfectly, and performance remained high. The experience reinforced a crucial lesson: more optimization is not always better.

Pro Tips to Avoid the Same Issue

• Always test checkout functionality when modifying caching settings
• Avoid using two cache plugins unless you’re 100% sure about their roles
• Use developer tools or incognito mode to test behavior without cache or cookies
• Exclude dynamic pages like cart, checkout, and account from any kind of static caching
• Review your .htaccess file for conflicting rules

FAQs

Q: Can I use SG Optimizer and WP Super Cache together safely?

A: It’s not recommended. Both plugins perform page caching among other tasks, and this redundancy often causes unexpected behavior — especially on dynamic pages.

Q: Why was only the checkout page affected?

A: The checkout page in WooCommerce relies on session data and dynamic scripts. When cached as static, it loses the ability to manage user-specific content, which breaks purchase flows.

Q: Didn’t SG Optimizer exclude those pages automatically?

A: Yes, SG Optimizer does exclude checkout-related pages by default. However, WP Super Cache does not, and if you’re using both, WP Super Cache can override or bypass exclusions leading to conflict.

Q: What’s the best practice for caching in WooCommerce?

A: Avoid static caching plugins that don’t recognize WooCommerce as a special case. Choose one optimized plugin (preferably SG Optimizer if you’re on SiteGround), and ensure that dynamic URLs are excluded from cache.

Q: How can I test if a page is being cached?

A: Use browser developer tools, observe the headers, or install a cache inspector plugin. Look out for cache-control and x-cache headers to see if the content is being delivered from cache.

Q: Is it safe to modify .htaccess manually?

A: Yes, but with caution. Always back up your .htaccess file before making any changes, and understand the rules you’re modifying to prevent breaking your site or exposing it to risk.

Conclusion

The quest for speed and performance shouldn’t compromise core functionality. This real-life case showed how even well-intentioned optimizations can lead to failures if not carefully evaluated. Using two caching and optimization plugins simultaneously may seem beneficial, but without granular control and awareness of what each does behind the scenes, it can result in costly downtime and lost sales.