Invisible blocks

If you see an invisable block, usually found because there should be a block where there isnt, or you can see the outline of it but you cannot see the block, then you can fix this by placing a block next to it. That should make it appear, if not then use the middle mouse button in creative mode to select the block, then break and replace it.
Usually this problem appears with the world files (when trying to import them to the server) to prevent this problem from being used instead, the schema.
Good to know: You can create a support ticket, describe your problem and, send proof of purchase so that you can be provided with the correct and repaired world