Question

An issue was added to the structure. Afterwards, the issue was moved in Jira to another project. Now the issue cannot be found in the structure, either by summary or by the new or old issue key. What happened?

Answer

There may be a couple of reasons for this:

The New Project Is Not Structure Enabled

Make sure the project where the issue was moved to is enabled for Structure. Structure ignores issues in the projects that are not Structure-enabled, so the moved issue is ignored as well, as if it ceased to exist. If you need this issue in the structure, either include the project where the issue resides now into the list of Structure-enabled projects or move the issue to an already Structure-enabled project (such as the original project).

The Issue Was Removed Based on Automation Rules 

If the structure was built using Generators, make sure the issue's new location satisfies the rules of your Insert and/or Extend generators. If it does not, you will need to change your generator rules or move the issue.