Hi, I've found that the problem that is NOT RELATED to StartIsBack++ but is due to a Microsoft Update. Unfortunately I installed the new version of StartIsBack++ the same time I applied the Microsoft patch so I believed that v2.9.13 has a bug related to taskbar icons. Following you can find the bug details confirmed by Microsoft.
"KB5003214 update is causing issues with Windows 10 taskbar
This is happening to users running Windows 10 May 2020 Update (version 2004) or newer with KB5003214 (optional patch) installed. One of the affected users told us that their taskbar is messed up with icons within the system tray going blank and overlapping, especially when News and Interests feature is enabled."