Hi all!
We are still investigating the issue, but I can confirm that using the tactics Sabotage, Blitzkrieg, Demolition, Barrage or by deploying airplanes to destroy a castle quickly will result in not receiving the full amount of points towards the event. As we are still investigating, our support team advises keeping an eye on your progress in case there are other scenarios in which progress is not awarded.
Due to the limited timeframe of events in general, we have no way to correct this before the event ends. As such, we want to make this information known so that everyone has ample opportunity to participate in the event and continue progressing towards its rewards. Good luck in your upcoming battles!