Explanation
When an org hits the account product period forecast record limit, new products cannot be added to account forecasts automatically. This means that when a user recalculates a single account forecast or all account forecasts, the new products are not added to the forecast. Also, if a user manually adds a new product to an account forecast, the product will not be included in the forecast calculations. The user will see a warning message indicating that the product is not calculated. Toresolve this issue, the user can contact Salesforce Customer Support to request an increase in the limit. References: Salesforce Help: View the Data Volume Usage, Defined Limits, and the Percentage of Limit Used for Account Forecasts, Salesforce Help:
Considerations for Working with Manufacturing