This is quite a common issue when people from the same household play at the same casino. Sharing the same IP address should not, however, be the only reason for voiding winnings, I'd say.
Furthermore, what you described sounds more like a shared household issue than a multiple account problem to me, sadly, both topics are close to each other.
Breaching the multiple-account rule means that a certain player has created more than just one allowed account. The first indicator that the player possesses more than one account is the IP match.
Now, why is this supposed to be a problem?
Because in times when bonus hunting was a lucrative thing to do, such hunters used to create more accounts to get access to welcome no deposit bonuses, which are normally only available upon new registration. Such an approach was developed to get more than one juicy bonus of the same kind.
Casinos developed the multiple account rule to fight these practices.
We at Casino Guru always say that the most important thing to do, is to clearly define whether a player accused of breaching the multiple account rule actually gained an unfair advantage over the casino by creating more than one account.
"We accept that it is the responsibility of players to make sure that they don't create multiple accounts at the same casino. Not because we think it's the right way to do it, but because it's the industry standard, and we cannot penalize all casinos that don't enforce the 'one account per player' rule the way we consider best. However, we believe and hope that checking for duplicate accounts during account creation will become the industry standard in the future, and players will be better protected."
I know your situation is a bit different because the other account belongs to your wife, but the logic behind this "persecution" seems the same to me.
Based what I stated earlier, I partially understand casino's concerns. On the other hand, I think that unless it is proven that you both "worked together" to maintain an unfair advantage by abusing the bonus system or any other action considered an abuse, it's just a normal situation where two people living in the same household also favour the same casino.
I'm trying to say that I'm convinced this situation is quite normal, and if the only reason for voiding your winnings is because your wife played in the same casino, so both accounts provided matched in IP, in my opinion, it's not enough to void your winnings.
Did anyone from the casino ever mention any other concern aside from the IP, please?
One way or another, browse this article called "Casino Guru's Fair Gambling Codex", point "11. Player verification and duplicate accounts" 👈 please
I'd say it's highly related to your situation; hence, I think it might be worth a look.
From my perspective, since you submitted a complaint in the past, I bet you are quite familiar with this option. Maybe it would not hurt to create another one now, because based on the Fair Gambling Codex, a more thorough explanation from the casino's side can't hurt.
What do you think?