Make sure the entry is EXACTLY the same as the menu item. It used to be “Save as PDF…” but was changed to “Save as PDF” (no ellipsis) in Sierra or High Sierra.
If you edit the shortcut it should work as it did before.
I haven’t made the jump to Mojave yet, so maybe the menu item has reverted to “Save as PDF…”
I know I had to delete the ellipsis some time back.
I can confirm this works on Mojave if you follow MacSparky’s post regarding changes needed for (High) Sierra (i.e. removal of the ellipsis from the menu item).