Setting up a WordPress Multisite network offers scalability and convenience, especially when managing multiple micro-sites under a single domain. However, even the most efficient systems can encounter hiccups that confuse even experienced developers. One puzzling issue occurred during the theme demo import process—everything was smooth on the main domain, but the import consistently failed on a subdomain site without showing any errors.
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TL;DR (Too Long; Didn’t Read)
The issue of a theme demo import silently failing on a WordPress subdomain was traced to a sub-site-specific memory limit restriction. While the main domain handled the demo import without issue, the subdomain ran out of memory but didn’t return an error. Increasing the PHP memory limit specifically for the sub-site resolved the issue. The fix highlights the subtle but impactful differences in resource allocation across a Multisite network.
Silent Failures: When There Are No Clues
It all began like a typical workflow: set up a WordPress Multisite network, create a few subdomain sites, assign themes, and import demo content to quickly prototype designs. The main domain worked flawlessly, successfully pulling in demo layouts, widgets, menus, and even media files. But when attempting to replicate the process for a newly created subdomain site, the demo import tool quietly failed.
No logs were written, no warning or error messages flashed on screen, and nothing unusual appeared in the server logs. Just an empty site where a fully built demo should have appeared. The process completed “successfully” according to the plugin interface, but the front-end told a different story—no widgets, no pages, not even a menu structure. The task had apparently finished, but nothing had actually imported.
Initial Troubleshooting Steps
The first instinct was to check the plugin compatibility and active themes. The same plugin and theme worked flawlessly on the main site, ruling out plugin errors. Next, file permissions were verified across the installation. Database access, user privileges, and even DNS propagation were all examined. Everything looked perfect on paper.
Manual demo content import was then attempted via WordPress’s native tools—still a blank site. Import logs also appeared to truncate unexpectedly, suggesting something was crashing the process, but again, nothing got logged.
The Hidden Culprit: PHP Memory Allocation for Sub-sites
Finally, deeper inspection of server resource configurations revealed the root of the problem: while the main WordPress installation had a robust PHP memory limit of 256M, the sub-sites didn’t always inherit the same resource settings. In this case, the specific subdomain had a memory limit of just 64M, far below what was needed to process large theme demo imports, which include images, post types, Masonry layouts, and a myriad of elements.
Though WordPress Multisite is designed to allow distinctive user roles and themes per site, less attention is often paid to back-end PHP limitations at the sub-site level. These memory restrictions can prevent demanding processes—like demo imports—from completing, without necessarily crashing the server or displaying a visible error.
Why There Was No Error
Import plugins often rely on AJAX calls that silently fail when PHP scripts terminate prematurely due to memory exhaustion. Servers configured to handle such terminations without displaying errors result in a seemingly “complete” import process with no actual data migration. This silent failure mode created the perfect storm of confusion.
Without an explicit timeout or error message, the issue appeared to be a mystery until memory profiling tools were introduced, revealing that the script was hitting its ceiling quite early in the process.
The Fix: A Targeted Increase in Memory Allocation
Once the problem was identified, the fix was straightforward: increase the PHP memory limit for the subdomain site. This was achieved by adding the following line within the wp-config.php file placed in the root of the WordPress install:
define('WP_MEMORY_LIMIT', '256M');But because Multisite doesn’t automatically apply this to individual sub-sites, a more precise fix specific to the subdomain was crafted using conditional logic. For example:
if (strpos($_SERVER['HTTP_HOST'], 'subsite.yourdomain.com') !== false) {
define('WP_MEMORY_LIMIT', '256M');
}
After saving and reloading, the demo import was reattempted—and succeeded within moments. All pages, images, templates, and widgets finally appeared, confirming that the import tool had been silently failing due to lack of allocated memory on the subdomain.
Lessons Learned
While WordPress Multisite can be incredibly powerful, it also demands close attention to server-level configurations. The assumption that sub-sites inherit all capabilities of the main domain can lead to blind spots, especially when dealing with resource-intensive tasks like demo content importation.
This experience underscored several key takeaways:
- Monitor Resource Usage During Heavy Processes: Use tools like New Relic or Query Monitor to understand what’s happening during imports.
- AJAX-Based Import Tools Can Fail Silently: Always verify that what “completes” actually imports.
- Sub-sites May Not Share All Configuration Settings: Check memory limits, execution time, and upload size for each subdomain individually.
- Error Logs Aren’t Always Helpful: When there’s a silent failure, monitoring tools or debugging PHP itself may be the only revealers of the root cause.
Conclusion
The silent failure of WordPress theme demo imports on subdomain sites within a Multisite installation was due to a subtle oversight—a lesser memory limit on the subdomain. Resolving it didn’t require plugin changes or code overhauls, just a bit more memory. It’s a reminder that sometimes, the devil is in the configuration details, and even small resource differences between environments can have disproportionately disruptive effects.
Frequently Asked Questions (FAQ)
Why did the theme demo import fail only on the subdomain?
The import failed on the subdomain due to a lower PHP memory limit that didn’t match the main domain’s. The resources were insufficient for the heavy data operations required by the demo content.
Why was there no error message or warning?
PHP processes sometimes terminate silently without returning detailed errors, especially during AJAX calls. This makes tracing problems like memory ceiling issues more difficult without external monitoring tools.
How can I check PHP memory limits on my WordPress site?
You can use plugins like Query Monitor or add phpinfo() to a custom PHP file to see active memory limit settings. Some themes or host dashboards also display these values.
Does increasing the memory limit for one sub-site affect others in a Multisite?
Not necessarily. You can include conditional logic in your wp-config.php file to adjust memory limits per sub-site based on domain or path.
Is 256M always enough for theme demo imports?
It depends on the complexity of the theme. Some might work with 128M, while others with rich demo content (sliders, images, layouts) may require more than 256M. Always test and monitor resource consumption during imports.