Hi,
The search override feature usually does not work, if there is some custom code involved or some major customization on the results page. Using multiple search/filter plugins can also conflict (override each others results), which could potentially lead to a seemingly malfunction.
There is also this option to try out, to force a more agressive override.
As far as I know Divi follows the standard programming guidelines, and does not do any funky coding for the results page, to allow search plugin to override it. I recommend checking if there is any custom codes used, or maybe if there is any other search plugin active.