1. Check if View -> Show -> Line Numbers is checked in the menu bar at the top of the document.
2. If it is not, check the box in the menu bar to enable the feature.
3. If the line numbers remain hidden in only certain sections, use the mouse to double-click on each section to select it, then re-click the box in the menu bar to reactivate the line numbers for the selection.
4. If the line numbers do not show up for the paragraph section, try selecting the paragraph and activating the numbering for it.
5. If the issue still persists, double-check the tools used for the document – some tools may not display line numbers.