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the main reason for not propagating grids sometime is view crops, just disable them on both (all) views temporarily.
The reason Propagate Extents is not available in views that are cropped is that the a crop boundary already affects the display of grids (and levels). When the crop boundary is invoked in a view that makes it special, unique or different from other views. Propagate Extents is only eligible to adjust a grids appearance in views that don't have a relationship with a crop boundary already. 🙂