It happened few times for my computer that some application icons were not displayed properly: Firefox, Virtualbox, JetBrains PyCharm, GoProStudio, Google Chrome.
Here is the solution I found at :
Here’s a slightly quicker version of the instructions.
1. Press Ctrl-Shift-Escape to get the task manager.
2. In the Processes tab, click on explorer.exe and click End Process. You’ll get a confirmation dialog. Click “End Process” to confirm.
3. From the File menu (still in the task manager), choose New Task (Run…).
4. Copy/paste/enter the following command in the run box:
cmd /c del %userprofile%\AppData\Local\IconCache.db /a
5. Open the Run box again with File –> New Task (Run…). This time, enter this command:
6. All should be okay now. Open the Start Menu and confirm that your icons are fixed now.