This is very very strange. While working from home, one day – each icon i clicked started disappearing. Very strange. After much analysis, i found out the solution. Due to lack of time, just posting the steips :
1. Right click. Just make sure the option is selected.
2. Click on the dropdown, and select the options that lead to resetting the toolbar.
3. Confirm and then see if all the icons appear.
Have a great day and keep rocking!!