Oh don't worry, this is actually quite common! From what I've heard, it's usually either high lipase activity (a natural enzyme that breaks down milk fat) or oxidation, lipase tends to give a more soapy smell, while fishy or metallic usually points more toward oxidation, though both can overlap. Either way, the milk is generally still safe, and the real question is just whether your baby will accept it.
The key thing I've heard from other mums is to try scalding your milk before freezing future batches, you heat it just to the point of small bubbles at the edges, then cool it quickly before storing, and that helps deactivate the lipase before it has a chance to break down the fats. For the stash you already have, some babies still take it fine even with the altered taste, so it's worth trying a small amount first before you decide to discard the whole lot.
That said, since it does touch on feeding your baby directly, it's worth running it by your PD or a lactation consultant just to be sure, especially if the smell seems off beyond the usual lipase or oxidation range.
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