Last fall every batch of soap I made (a batch is 50 bars) ended up with DOS. I cried and cried so threw away all my oils I bought in the 35 pound containers and started fresh with new smaller containers from Columbus Oils in Chicago. Stopped using canola and using only Olive with Castor for 1/2 my oils. Haven't had DOS since and really didn't have the heart to try experimenting into which oil it was but it was every batch. You can imagine what I lost with not to mention time but I only use essential oils. Since that time I've been making 1/2 batches because I am still freaking out. I also wonder if those 35 pound containers they send me sat in some hot warehouse for some time waiting to be shipped. Love working with Columbus but another time when I order Castor Oil they went me Avocado Oil and I didn't look at the label so lost that batch before I realized what I was doing.
Oh boy, bountifulsoaps, how aweful! That's heartbreaking to lose every single batch. I'd have done the same and started over with new oils. Since we can never know how long the containers have sat and in what conditions, it can be a crap shoot. Have you considered adding EDTA, citric acid or sodium citrate to your batches? ROE added to the soft oils when opening a new container might be useful too.
My last 3 batches of laundry soap developed DOS which really has me baffled (and angry!). It's simply 100% CO and -1% SF. No additives. I made another batch yesterday, using a new container of CO, and added EDTA at 0.5% total batch weight. Hopefully this fixes the problem for me. I hate the waste of ingredients and time when I have to toss soap due to DOS!