500 error on admin-ajax.php

Like a number of other people on here, I was also having the admin-ajax.php 500 error. I’m on GoDaddy hosting and using Cloudflare.

While I do have it working again, I’m not sure what initially caused the problem so hopefully there are some clues in what I did to fix it.

Basically, Optimize All Pictures just stopped working and when I tried to start it again I got the spinning clock and admin-ajax.php error.

The first think I did was check the media library to see what file it had stopped on. It was a 4MB PNG file that wasn’t even being used on the site, so I deleted it from the media library. Unfortunately this didn’t fix the problem. I noticed that the next file after the stuck PNG that was an SVG, so I disabled reSmushit for all SVGs, but that didn’t fix the problem either.

Finally, I turned on the log function and ran the Optimize All Pictures again. As usual, the clock spun and there was the admin-ajax.php 500 error. The resulting resmushit.log file only has two lines:

[19-06-2018 03:53:13] Bulk optimization launched for file : /path/to/photo.png
[19-06-2018 03:53:13] Revert original image for : /path/to/photo.png

The photo.png file was the one that I’d already deleted from my media library. Indeed it was deleted from the media library, but I checked the path and the file still existed. I had to manually remove it and it’s thumbnails using FTP. Only then did the Optimize All Pictures to start working again.

Hopefully this helps fix whatever this issue is.