Hello, I am Leonielhou, an Independent Advisor and a user like you, I am happy to help clarify any questions you may have.
this behavior could be due to the calculation mode being set to "Manual" instead of "Automatic." When the calculation mode is set to manual, Excel only recalculates formulas when you explicitly request it by pressing F9 or clicking the "Calculate Now" button.
You can check the calculation mode by going to the "Formulas" tab in the ribbon and looking at the "Calculation Options" section. If it's set to manual, simply change it to automatic and the formulas should update automatically when the lookup value changes.
Another possibility could be that the workbook has become too complex or large, causing it to slow down and not update the formulas immediately. In this case, you can try breaking down the workbook into smaller, more manageable files.