Crash on launch, appears to relate to gameplay programmnig

Perhaps, this post doesn’t belong in this section, but searching the error in my call stack,

LowLevelFatalError [File:d:\build++ue4\sync\engine\source\editor\animgraph\classes\AnimGraphNode_SkeletalControlBase.h] [Line: 164] Pure virtual not implemented (UAnimGraphNode_SkeletalControlBase::GetNode)

I found and responded to this thread appearing in this section, alas to only get a partial answer. To provide a bit more context, this crashing follows steps I had taken to overcome an earlier case in which in Editor, not in gameplay but just static, my screen would go black or present artifacts, sometimes crashing. The behavior persisted in other projects, but not in a new project. I began with Nvidia techs, they ran MSI Kombuster, video card seemed fine. We tried a new user, maybe bad registry keys, link to DirectX, other possibilities, but that itself produced too many new problems to mention, so I reset Windows, only installed Epic Games Launcher, loaded 4.20.2 (BTW, same behavior in 4.19.2 and 4.20.1), now getting the crashing on launch. If not system, if not the GPU, if not the engine, then what? I should add, this crashing on launch doesn’t happen with a new project, but to isolate against a corrupted project, I restored from a backup a version that was stable.

Thanks for your time.