When you insert a comment in a spreadsheet, you only see an indicator in the cell. The comments will display only when you click or hover on the cell. If you have different settings and want this function back, please see the steps below:
Step 1: Click the "File" Tab from the ribbon;
Step 2: Click "Options" from the left navigation menu;
Step 3: Click "Advanced" from the left menu in the dialog box;
Step 4: Check "Indicators only, and comments on hover" under the section of "Display";
Step 5: Click "OK" at the bottom to apply the changes.