Hi Naoto,

I cannot reproduce the issue. This is what I tried on a clean install.

1. Open de posts overview page
2. Add a lot of custom columns
3. Just click the search post button

Without searching for anything, my results are just the same. Can you check if sorting is active (reset button is visible on top of the overview) and if so, can you reset the sorting. Or did you filter on a column?

It’s also possible that there is another plugin that also does something with search query. Can you try to disable some other plugins to see if the conflict is with another plugin?

I tried the plugin on a clean install and even then I’ll get the error message.
This seems to be an issue for the Search Everything plugin. We can’t do anything to solve this issue.
Maybe you can report this issue on the plugins support page.