Render Dragon has been properly optimised after this current update, but all that remains is likely an autosave lag spike which occurs every 38 seconds. This lasts around 500 milliseconds. Or this could be some backend garbage collection, I don't know C++ that well. I think it has something to do with the renderer flushing itself out and/or writing to memory, I have no idea. But Render Dragon is getting better. This bug happens on all platforms. (I tested on Android as well)