So what you’re saying is that the index is for all sites (including posts, custom posts, pages, products, custom fields i.e.) in the network and each search instance (is the search instance the same as a search form?) can limit what sites to search in? Is that correct?
We can’t get your instructions to work since there are no sites available in that box (see attached screenshots). What could be wrong? We have created this search form/instance on our main site in the network and also the index.
Also if we search on main site we get all results from main site, on the other hand if we go to “site 2”, “site 3” or any other site in our network we get results from our main site but not from any other site. We are getting search suggestions on “site 2”, “site 3” and other sites than main site, but if click on that there are empty results. What could be wrong?