Check your Clutter folder. The Clutter folder is found the left panel. If it is not immediately visible, click More. If your missing emails are in the Clutter folder, turning off automatic clutter filtering may resolve the problem.
Solution 2: Check the filter options
Check your Inbox message filter.
Click on the Filter drop down on the top right of your Inbox display.
Make sure All is checked in the Filter section and Date is descending in the Sort by section.