Maybe there was something wrong with only that bag? Are they all that way or just one? Also, freeze within a day to keep it as fresh as possible. I wouldn't dump your whole stash unless you test more of them. How long did your husband have it out and how did he thaw it?
I checked one from 11/10, 11/18, 11/28, 12/9, 12/18, 12/22 ALL bad. I warmed them with hot water just like DH does too. All BM was frozen as it was pumped. I would pump and then put in the bags right away and deep freeze in a chest freezer with ONLY the BM in it. He had just thawed that bottle I initally tried. Typically dont leave it sitting out and take from freezer to hot water, warm, and feed.
We followed directions to a t and it sucks but Im 99.9% my stash is garbage. Although, I read that you can still donate it so Im looking into that now too.