Sous vide topside beef- what went wrong?
Your process is in line with the practice of sous vide and cooking beef topside roast, which leads me to believe that the culprit is your particular cut of beef.  Did you purchase at a reputable butcher shop, or pick it up from the shelf of a grocer?  In either case, it might be worth a conversation with a knowledgeable butcher for some advice for next time.  In the mean time, maybe mince or grind the leftovers and use for a pasta filling like an agnolotti.