Looking at the front-end the search configurations look very similar to me, but I’m not able to check the administrator area nor the files via FTP.
Can you please check both back-end and FTP account permissions? I’m suspecting some kind of minor difference in the configuration of the search instances. Once I get to debug the final queries, I will see what the problem is.Best,
If you like my products, don't forget to rate them on codecanyon :)