Users appear to drop out of Funnel to another domain or subdomain
If one or more of your funnel steps are defined as URLs from another domain or subdomain, and your tracking code isn't customized for cross-domain tracking, users will appear to drop out of the funnel.
For example, suppose you set up your funnel as follows:
Goal URL: www.example.com/jkl.html
Step 1 (Required step): www.example.com/abc.html
Step 2: www.example.com/def.html
Step 3: www.example.org/ghi.html
If the tracking code has not been customized for cross-domain tracking, users appear to drop off at Step 2. This is because a new session is created when the user goes from www.example.com/def.html to www.example.org/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.