Same. I had this issue a week ago. Created a thread about https://answers.ea.com/t5/Technical-Issues/Error-721/m-p/7341250 and closed it myself
After messing with windows restore points, enabling and disabling various service it finally started to work. And this error just occurred again. This is so bizarre. Not just only this game has this issue, but the work around that worked for my system. For example, I reinstalled windows completely at some point a week ago just to be sure, and it helped. Literally right after disabling windows update services and telemetry services the game gave me the 731 error. Then I restored. Then I tried it again but in different order. Same result. Then I tried it again and again up until the game started to login in online successfully, but with all the windows 10 bs off. I still don't know what caused it. Firewall is off. Origin services are working. Internet is fine. Router is fine.
So again, game was working fine then it decides to stop working and give the Error code 721 for no reason. Steam games are working. Battlenet games are working. Everything is working but this game. I don't know what to do.