The Coco event started on October 30, 2017, and ended on November 27, 2017. It was sponsored by the film Coco. It featured two free catalog items, and three prizes. The games that were featured were Meep City, ROBLOX Escape Room, and Quill Lake.
Although the event was scheduled to end on November 22 which was the day the movie came out, it did not end until November 27. It is unknown why ROBLOX left the event running until then.
(Coco spoilers!) Ernesto de La Cruz's guitar is actually Hector's guitar, as revealed in the film. Since the film wasn't released in the USA when the event started, the guitar being attributed to Ernesto de La Cruz is justified.