We're already working on this!
It happens because there is a mission task that is counting points towards your event progression and it shouldn't. So actually, the server is correcting the points because you haven't officially earned them.
Our team of Zookeepers is working hard to identify which task is causing this. If you experience this and want to help on the investigation, just send us a message through the game support button and inform our Zookeepers! :)
Thank you for helping and see you at the Zoo!