If you are building from source, two small changes are needed to fix this for AnimNotify nodes.
In AnimModel.cpp, the Frames SnapType SnapFunction needs to return a time in seconds, not a frame number:
And the MaxSnapDist constant inFNotifyDragDropOp::GetSnapPosition needs to be much much larger than 5. 500 works well for me.
With just these changes, it is still not possible to snap Sync Markers to frames, but that can be fixed by modifying FNotifyDragDropOp::OnDraggedso that it performs the snap logic for all SAnimNotifyNode types, an exercise I leave to the reader.