Following yesterday’s patch a bug was introduced that is causing FPS to drop and response lag if an empire has many planets.
We’ve identified the cause of this and are working on a fix at the moment. As soon as it’s ready we’ll push out a hotfix.
Apologies for the inconvenience. I’ll update you as soon as I know more.
Update: this should have been fixed in today’s server maintenance. Please let us know if you still experience this issue after updating to the latest patch.