Search is broken after updating search_api_solr from 8.x-2.7 to 4.1.4 My Drupal site has a search form, which connects to a Solr index. All of this was working smoothly.
But then I updated drupal/search_api_solr from 8.x-2.7 to 4.1.4 (which also required me to update drupal/search_api from 1.13 to 1.17) – and now the search is broken. Specifically:

The &quot;default&quot; search results – the ones that are displayed when I first land on the search page, before entering any search keywords – are now different.

When I do enter keywords and submit the search form, it always returns no results. This happens with any keywords, even when there are definitely items in the index that should match.


Here's what I've already tried:

Cleared the Drupal cache repeatedly (of course).
From the Drupal configuration dashboard, I have:

Confirmed that the Solr server and index are configured correctly, and that Drupal is able to access them.
Deleted everything in the index, and re-indexed. (This appeared to complete successfully.)
Examined the AJAX response to the search submission, and compared it to the response on a working instance of the site. (The only difference is that HTML returned on the working site includes results, and the HTML returned on the broken site doesn't.)


Looked for upgrade guides for the search_api and search_api_solr modules. (I haven't been able to find any.)

Any suggestions? I'm running out of ideas here.
After the latest search_api_solr module update you need to update config files on your server, as there is a new field added.
If you look into the update log you will find the below message.

A new Solr field type has been installed due to configuration changes. It is advisable to download and deploy an updated config.zip to your Solr server.

You can find the additional information on how to update server configs from the below link.
Upgrade Search API Solr 
Even after checking above points if you are still getting issues, check whether it is due to varnish.
And also run cron once and clear drupal cache after cron and check results again.