When Reorder Point field is hidden on a Custom Inventory Part Form and a user disabled Advanced Inventory Management feature to switch to basic/simple Inventory Management, Reorder Point field can no longer be displayed on a Custom Inventory Part Form.
To show Reorder Point in a Custom Inventory Part Form:
1. Navigate to Setup > Company > Enable Features > Items & Inventory
2. Go to Inventory section and enable Advanced Inventory Management feature then Save
3. Navigate to Setup > Customization > Entry Forms
4. Click Edit link beside the name of the form to be edited
5. Go to Fields tab > Purchasing/Inventory subtab
6. Mark Show checkbox for Reorder Point then Save.