A blank sailing is a sailing that has been canceled by a carrier. It can also mean that they are skipping your port of loading or destination.
Blank sailings happen when demand for space on vessels is low. When there is less demand, carriers need to make sure their sailings make sense economically and keep rates up.
Normally you can expect blank sailings during Chinese New Year and Golden week. Factories have been closed. Now with the Corona crisis happening, we expect to see a historically large amount of blank sailings happen.
If your cargo is cancelled, your cargo will be moved to the next available spot on a vessel. People call this "your cargo is being rolled" or a rollover.
There isn't much you can do about other than giving Shypple a forecast well in advance during peak seasons and now the Corona Crisis.