Users appear to drop out of Funnel at step to other domain or subdomain
If you have funnel steps that include URLs from different domains or subdomains, and your tracking code isn't customized for cross-domain tracking, then your report data indicates that users who follow those steps from one domain to another drop out of the funnel.
For example, suppose you set up your funnel as follows:
Goal URL: www.secondsite.com/jkl.html
Step 1 (Required step): www.firstsite.com/abc.html
Step 2: www.firstsite.com/def.html
Step 3: www.secondsite.com/ghi.html
In this example, if the tracking code is not customized to track across multiple domains, then users appear to drop off at Step 2 because a new session is created when the user goes from www.firstsite.com/def.html to www.secondsite.com/ghi.html. In the new session, Google Analytics has no knowledge of the user having completed Step 1 because it was done in the previous session. As a result, there is no data to indicate that the user converted the goal.