That's a bug that I haven't seen before. It seems to happen during scene postprocessing (probably during the bloom effect). Since we didn't expect this bug, we didn't add any option to swith on/off the postprocessing stages. Could you tell me the browser and operating system you use and the graphics card in your computer? Thank you.
Mozilla, nVidia GF106M, driver v390.116 . Turns out there's a heap of errors written to the console.log, I put them in a pastebin. https://pastebin.com/XX7JRUFs