I have a joint checking and savings with another person to whom I am not married nor have any legal relationship under the law, except, we live together. I did not receive notification of a summons (and yes, I sent a letter for disclosure, it was not responded to) a judgement was rendered against me and a restraint placed against the account. I have since agreed to a financial settlement in lieu of vacating the judgement to expedite the process. My question is how can an account where I am not the primary but am listed on the account be frozen if someone else to whom I am not married nor related to?

Because the other person had a judgement against them. And his money was frozen, so this account was frozen because he had his name on it.

You would have had to go to court and prove what part of it was your money. This is very common.

And although not married, you do have one legal relationship, you have a joint bank account, so you are partners in this money.