Is zakat obligatory on money that has reached its nisab and was accumulated in anticipation of the government seizing it, knowing that the accumulator may face financial hardship, take from it, and then return it?

You must inform the authorities responsible for the error that occurred to restore the right. Otherwise, the money is a trust (amanah (definition)) and may not be disposed of. If the state deducts from your salary, it is permissible for you to take an amount equal to what was deducted. This money is not subject to zakat (definition) as long as it is not owned by you. If the state permits its utilization, it becomes a debt upon you, and it is more cautious to pay zakat on all the money in your possession without deducting the debt.