Moonstorm has a chance to disappear

This is quite common and it's been raised a few times. Another bug raised was here and here.

If you dont have all the things you need to build the experiment for the boss, the community has decided to spawn in the items you need for the boss and when you defeat it, the moon phase and everything else will go back to normal. And placing the items back in the fissures will bring the storms back. Hope that helps as a temporary fix

I experienced the same issue on my dedicated server today. Had previously completed the moonstorm event and then shut down the server. When I rejoined today there were still eternal full moon but no active moonstorms in the world. Had to spawn in mats because there was no way to restart event.