*while* resizing the window in the first few screens, the resizing event produces a bunch of garbled graphics, which then resolve when the resizing finishes.
I've seen this in Safari/Mac, also; can't recall if it happened with other clients. Not sure if this might be a client-side thing, as I know I've seen it happen outside of Glitch as well, usually when I'm low on free memory.
I'm not sure how much we can do about this, but I'll talk to our dev team to see if there's any workaround or solution. In general, though, when you're resizing the window, you're not playing the game, so I'm not too concerned about this issue, personally.