He is using zara 

@club4dog

I have the same problem with the veronika theme.     

i use many themes, also zara and veronika and there is no problem at all if you do it right

Could you send me URL where is highlighted item in search? Problem might be that highlighted block is overcovered by different block.

https://www.radio7menomeno.it/tolettatori/negozi/test-con-evidenziaziazione_i26


this is a test site, where I do the tests before putting them on the primary site club4dog.com

@club4dog
Is this listing highlighted? If yes, you are not using latest theme version and you must add highlight_class hook.
Plugin itself contains detail description how to do it, if you do not want to update.