Try the following in order until the issue is resolved:
  1. If you added a query from the Add > Multiple Constituents button, check to see if the records are/are not in the query results.
  2. If the records are in the query, but aren't in the Invitation process, click Add > Multiple Constituents, select your query again, and click the Exclusions button.  Remove any solicit codes or unmark the box to exclude inactive and deceased constituents, if you want to mail to everyone in the query.
  3. This may be due to selecting your Address Processing Options, if a constituent is missing, go to their record and ensure they have a valid address on their record
  4. Ensure your householding options are not causing constituents to be excluded/included, more information about these options can be found in our help content about the Add Invitation Screen