Running 4.25.1 here. I activated the composure plugin, and now my map is incredibly sluggish. Deactivating composure once again returns performance to the editor. The map is quite large and complex but still performs fine in the editor. I wondered why all of a sudden it got to be unusable, and then remembered I started using composure. I tried disabling the plugin and now the editor performs flawlessly and smooth. It basically became unusable even at medium scalability.