Hi,
In Odoo 19, overdue invoices may stop being attached to follow-up emails even if no changes were made to the database. This often happens because the mechanism for attaching invoices relies on generating PDF reports through the account_followup.report_overdue QWeb template, which may not be correctly accessible or could be missing.
Even if the follow-up levels and email templates are correctly configured, the scheduled action responsible for sending follow-ups may fail. It’s important to check Settings → Technical → Automation → Scheduled Actions → Follow-up Mail to ensure it is active, review the last run and next call, and examine logs for errors.
Testing manual follow-up sending from a customer form can help isolate the issue. If manual sending generates the attachment correctly but automated emails do not, the problem is likely with the scheduler, access rights, or PDF generation. Restoring the correct report template and ensuring the scheduler runs properly usually resolves the issue.
Reference:-
* https://www.odoo.com/documentation/19.0/applications/finance/accounting/payments/follow_up.html
Hope it helps