Hi!
Thank you for the details, it helps us a lot!
It looks like you have an incorrect mod_rewrite rule or a redirection function in your code setup incorrectly. When I tried to visit the original results page, for example: https://www.thecandleboutique.co.uk/?s=apple
I am redirected to that wrong URL.
You might be using a custom code or an apache mod rewrite condition to make the search URLs prettier via redirection, but it seems like there is an error in there and it adds an additional “/?” string at the end of the URL, which creates the error message.