WP‑Optimize Fatal: implode() Argument #1 must be of type array – How to Fix

You’re hitting a known edge case in WP‑Optimize Minify where an internal array becomes null and implode() fatals under PHP 8’s strict typing. Here’s how to recover fast and fix it for good.

Quick recovery (get the site back)

1. Disable WP‑Optimize via WP‑CLI (preferred):

   wp plugin deactivate wp-optimize

   Then log in to WP admin. If WP‑CLI isn’t available, temporarily rename the plugin folder via SFTP to wp-optimize-old.

2. Once you can log in, reactivate WP‑Optimize, but leave the front‑end Minify features off for the moment.

Permanent fix (keep Minify, avoid the crash)

1. Turn off “Merge” for JS and CSS (keep Minify on). In WP‑Optimize → Minify:
   • Uncheck Merge JavaScript and Merge CSS.
   • Leave Minify JavaScript/Minify CSS enabled.

   Merging is the usual trigger here, and you don’t need it on HTTP/2/HTTP/3. You can confirm your site supports HTTP/2 and safely leave merging off.

2. Find and exclude the offending script/CSS. If the error only happens on specific pages (e.g., pages with a certain plugin’s shortcode), exclude that asset from processing:
   1. Open the page, press F12 → Console; click the red error to reveal a file path.
   2. Switch to Network, locate the same file, right‑click → Copy link address.
   3. In WP‑Optimize → Minify → JavaScript (or CSS), paste the file URL/path into Exclude from processing.
   4. Save and purge caches (see step 4), then retest in a private window.
3. Isolate by toggle (if you still see issues):
   • Temporarily disable Minify JavaScript only. If the error disappears, it’s a JS file. Exclude it, then re‑enable JS minify.
   • If it persists, try the same with CSS.
4. Purge all caches after each change:
   • WP‑Optimize → Minify → clear/purge minify cache
   • Your page cache (WP‑Optimize cache or a separate cache plugin)
   • Any CDN/host cache (Cloudflare, host‑level cache)
5. Update WP‑Optimize to the latest version. The issue was acknowledged by support; newer releases include improvements. Update the plugin, then retry with merging off and exclusions in place.

Why merging often breaks (and why you can skip it)

On HTTP/2/HTTP/3, merging many files into one can reduce performance and increases the chance of malformed bundles. Keeping minify on and merge off typically gives the best mix of speed and stability.

CLI and emergency commands

• Deactivate/reactivate quickly:

  wp plugin deactivate wp-optimize
  wp plugin activate wp-optimize

• Clear browser cache and test in a private window to avoid stale scripts.

FAQ

What exactly causes “implode(): Argument #1 must be of type array” here?

PHP 8 enforces strict types. If Minify receives null (or a string) where it expects an array of files, calling implode() fatals. Disabling merge and excluding the problematic asset avoids passing an invalid value into that code path.

Can I leave Minify enabled?

Yes. Keep Minify on for JS/CSS and turn off merging. If one specific file still breaks, exclude it using the built‑in exclude lists.

How do I pinpoint the exact file to exclude?

1. Open the page → DevTools Console → click the error → note the file path.
2. Use the Network tab to copy the file URL exactly.
3. Paste it into the Exclude box under WP‑Optimize Minify (JS or CSS).

Do I need to downgrade PHP?

No. This is fixable at the plugin/config layer. Keep PHP 8.x for security and performance; update WP‑Optimize, disable merging, and exclude problematic assets.

If you want us to isolate the breaking file and set the exclusions for you, we can help.