There is a current backend issue affecting some players opening chests (due to a mismatch in how some chests are stored in account data), though this is more likely to occur when you only have 5 chests remaining and would prevent these from being opened as an example. KNOWN ISSUE: Backend Error Preventing Opening Chests - #2
Too many requests being sent to the backend in a short time will result in a Backend Error. This is most commonly triggered when spam opening chests or re-rolling traits.
Al parecer el problema es solo con un cofre, porque despues de realizar una mision y abrir ese cofre, me di cuenta que lo seguia teniendo, puedo abrir el resto de cofres de forma normal, pero al abrir ese cofre de plebeyo me obliga a salir del juego con el mensaje “error de motor”.