I used it for the first time last month. It was given to my three does due February 12, 14, & 15. Only Chaos had a reaction. I heard last night about a new bottle each time.
Was it a new or old bottle? It was pointed out to me that the labeling indicates you need to use what you need and toss the rest (new bottle each time). Also it's possible the manufacturer changed something. Definitely conversation with your vet though.