This is usually because invoices and vouchers from a particular account series (e.g. an account series for internal entries, often reversals or vouchers) come into AIMZ as invoices, even though they should not be treated as project invoices.
Solution: You can set up the ignoring of an account series yourself:
Open Edit project (next to the project name) and go to Settings.
Enter the account series in the Ignored external accounts field. Invoices from this series will then no longer appear in AIMZ.
If you need help, AIMZ support can set up the ignoring for you. Support can also help you automate linking invoices from specific account numbers or production codes to the right account or production code. Read more about automatic linking in Invoice linking.