Thanks for bringing this to light, SS. Some time in November I bought some Hellmann's mayonnaise and I couldn't believe just how bad it tasted. I have been eating HM for some forty years, starting in England where it tasted just like it does here, and I have never been disappointed. I have tried Hellmann's omega-3, Lite and olive oil-based variants and have always gone back to the original product because it just tasted better. I didn't throw the latest stuff away, but I decided to give it a chance. Each time I tried it, the difference in taste was immediately noticeable, with a cheap oily taste - even when I just used a very thin film on a sandwich.
Wanting a solution, I finally decided to search the web and came across your post. I then called the 800 number on the jar and spoke to a Unilever rep who assured me that there had been no change whatsoever in the way that the product was made. This is at odds with the narrative on this thread, so I don't know what the true story is. All I know is that the mayo that I bought from a major supermarket (so spoilage is very unlikely) is very different when compared with the few hundred jars of HM that I must have eaten over the last forty years.