In some cases, some app will leave an un-removable blank icon on the Windows Taskbar after an unpin operation, like this one:win10 任务栏图标取消固定后原位置留空 I diden't tried the instructions in the post(cause I don't think it works), here is the way I used to solve this problem:

With my friend's suggestion I tried to use Precess Monator to analyze what Windows Explorer did with pinning and unpinning process, and I found these 2 interested paths: %appdata%\Microsoft\Internet Explorer\Quick Launch\User Pinned\TaskBar %appdata%\Microsoft\Internet Explorer\Quick Launch\User Pinned\ImplicitAppShortcuts After delete all useless Shortcuts in these folders and restart Windows Explorer, the problem is solved.

If you don't know how to restart Windows Explorer, search it.