This turned out to be a server side issue and was resolved by WPEngine.
I just tested your new version and it works correctly.
Thanks again
Thank you for a very useful plugin.
I’m happy to contribute to the community.
It turns out that the plugin was altered in versions 0.3.18 and 0.3.19 in such a way as to cause a database error on custom field searches.
When I reverted back to 0.3.4, custom field search worked perfectly for the wp-custom-search plugin.
