There is definitely an error message somewhere, but it's either supressed, or turned off somewhere. The ajax request returns a completely emtpy response, so the search looses the control at some point for some reason. In case of no results there should be something in the response body, so there must be an error somewhere.
Have you found out why is the no-cache header added so many times?
The only option I can see here is for me to check your back-end and debug the code through FTP. There is no error message, nor an indication of errors so the only option is debugging the code directly. Could you please provide temporary back-end and FTP access to the test server so I can debug through the code? You can upload them in a .txt file, it's not accessible to anyone but me and you.Best,
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