Tray icon is blank

Tray icon is occasionally displayed as a blank space. Although this blank space seems to be functioning as a normal icon: when I run the mouse over the blank space, I get "Wifi Guard" tooltip; and when I left-click the blank space, Wifi Guard app opens correctly.
Any idea what is causing this?

This can sometimes happen due to cached registry settings. We have a special batch file for fixing this issue.

Alternatively, you can follow these steps:

1. Press WindowsKey+R to open the Run dialog.
2. Type regedit, and press Enter.
3. Navigate to this registry key
   HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\CurrentVersion\TrayNotify
   and delete the values IconStreams and PastIconsStream.
4. Navigate to this registry key
   HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\TrayNotify
   and delete the values IconStreams and PastIconsStream.
5. Navigate to this registry key
   HKEY_CURRENT_USER\Control Panel\NotifyIconSettings
   and delete the entire key.
6. Restart Windows Explorer or reboot your computer.

This will refresh all notification area icons and reset all their settings, but it should resolve the issue.

In older versions of Windows only some of these keys may be present, for example only HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\CurrentVersion\TrayNotify. In such case, follow the instructions for the key(s) that you do have.

This appears to have solved the issue.
In the process, it also reset all my tray notification icon customization settings, which I had to redo, but other than that everything seems to be ok now.
Thank you