Just recently, the DO icon on the Windows Taskbar on the left monitor of a dual monitor system is different than the one on the right monitor.
The left monitor icon is a generic one, while the right monitor is the proper DO icon.
I'm running DO 10.2.0.0 (4645) X64; also running Display Fusion to manage the dual monitor setup. With Display Fusion off, there is no Windows Taskbar on the right display, of course, but the DO icon on the left display Windows Taskbar is still the generic one. Restarting DO makes no difference.
Is the icon pinned to the taskbar? Try unpinning it, restarting Opus, then pinning it again.
It may also be worth a try to reboot, then try Clear Icon Cache again. If Explorer didn't restart automatically then the cache may not have been cleared at all. Or you could try clearing it manually, which involves killing Explorer.exe and then deleting the C:\Users<your_user_name>\AppData\Local\IconCache.db file.
Problem solved!
You were definitely on the right track to clear the icon cache, but I had to do it manually. When I followed your last suggestion and restarted Explorer, the proper icon returned. (Funny thing is that the left monitor icon has a yellow orb; the right monitor is blue - not a problem, actually kinda cool).