Dedicated crawl target configuration has one or more invalid servers (SharePoint Server)
APPLIES TO: 
2013 2016 2019 Subscription Edition 
SharePoint in Microsoft 365
Rule Name: Dedicated crawl target configuration has one or more invalid servers.
Summary: Dedicated crawl target configuration has one or more invalid servers. This may degrade search crawl performance.
Cause: The URI is incorrect, or the server is not joined with a valid role to the SharePoint farm.
Resolution: Make sure the uniform resource identifier (URI) is correct, and the server is joined with a valid role to the SharePoint farm.
- Make sure that the URI is correct. A valid URI meets the following criteria:
The host portion of the URI should be the name of a server that has joined the SharePoint farm.
The URI Scheme should be HTTP.
The URI must not contain an absolute path.
For more information, see URI class.
- Make sure that the server is joined with a valid role to the SharePoint farm. The server can be any of the following:
Front-end
Application server
Distributed cache
Search
Custom
Single-server farm or a stand-alone server in the SharePoint farm
For more information, see Overview of MinRole Server Roles in SharePoint Server 2016 and Description of MinRole and associated services in SharePoint Server 2016.