Yesterday, on the Jade Ghost gate, I was on a Scarlet Fortress map, Depth 21. When we reached the final party button, we noticed something quite bizarre with the background. Object frames stayed on the background, fading after around half a minute.
NOTE: This is my Steam alt I use to post on the forums. My main is, shown in the screenshot, Pennzqwu.
It's those type of rendering issues we don't know how to solve. If this rarely occurs, then it shouldn't be a major problem.