Repro Steps:

1) Download the attached ConvertCanvasToGrid_Project, and open it in Studio.
2) Within MainPage.xaml, navigate in the hierarchy until you find the Canvas named "CONVERT_ME_TO_GRID_VIA_CONTEXTMENU"
3) Right-click on the Canvas, and from its context menu, navigate to 'Layout'-->'Replace With', and then select 'Grid'.

Observe how the positions of the Paths on-Stage are moved from their original positions.

4) Use Ctrl+Z to undo the change to make the Canvas into a Grid.
5) Drag the Canvas into the RootGrid, and delete the now empty Viewbox.
6) Right-click on the Canvas, and from its context menu, navigate to 'Layout'-->'Replace With', and then select 'Grid'.

Observe how the positions of the paths on-Stage are successfully retained.

Expected Results: A Canvas within a Grid can be successfully converted to a Grid whilst retaining the position of all Paths within.