Core maintainer of NppCSharpPluginPack here.
It’s pretty hard for me to diagnose your problem if you don’t share a link to your full codebase with me. However, it looks to me like you’re calling SetToolbarImage in the CommandMenuInit method, which I don’t think you should do. In the current version of the plugin pack, you may notice that in the beNotified method of UnmanagedExports.cs, the SetToolbarIcons method is called, which initializes all the toolbar icons for the plugin.
Truth be told, I have never studied the relevant sections of the Notepad++ codebase well enough to fully understand what’s going on with toolbar icons. I’ve just mostly gone with what worked in the old NotepadPlusPlusPluginPack.Net in this instance.
