I have tried a lot of formations, they have all been 4 at the back, the main one used though was 4231 with wingers and they were CMs not DMs, I had it on attacking, full backs support, defensive box to box, advanced playmaker, inside forwards, shadow striker, complete forward, lower tempo, pass into space, retain possession, close down more, tight marking, get stuck in, play out of defence, tried for about 40 games and conceded at least 2 in about 30 of them, all my defenders are good/leading prem ones tooYou will need to give more information if you want help mate, team, players, formation, mentality etc. the more you can tell us the more insight we might have.
To be honest i am having a similar problem though no where near that bad. Think this year more thought needs to be put into how you organise your defence then ever before.
I have tried a lot of formations, they have all been 4 at the back, the main one used though was 4231 with wingers and they were CMs not DMs, I had it on attacking, full backs support, defensive box to box, advanced playmaker, inside forwards, shadow striker, complete forward, lower tempo, pass into space, retain possession, close down more, tight marking, get stuck in, play out of defence, tried for about 40 games and conceded at least 2 in about 30 of them, all my defenders are good/leading prem ones tooWhat's your tactic, and for how many games have you run it? We can't know without knowing what team you are, how many you have at the back, whether you have midfielders set to defensive roles, your team mentality and shape, your instructions, how fluid the tactic is, and what your OIs are. If you throw men forward, you'll be leaky. You need good players to give more thought to stopping the opposition rather than helping you, one central midfielder or DMC must be primarily defensive, and don't throw your full-backs too far forward until you have better team morale. Look to see where you lose possession, and fix that combination of player roles. If the other team walks through you, see what narrower or wider instructions do. The same applies to closing down or not.