Hiya all am new to the forum and new to the Inibuilds a380 I hope I can get some help weird thing happened to me . During cruise the aircraft started over-speeding and the altitude dropped , the autopilot came off. I did use simbrief to do my flight plan and put everything in right in the fmc. Would anyone know what could have happened or what I may of done wrong . Would appreciate anyone help please. Picture below before everything went wrong.