gettingonabit have you had a virus recently? This happened to me several years ago. The weirdest experience. I couldn't smell bad smells at all, but things like washing powder, anything perfumed, good food smells, to me smelt like rotting corpse! ?I was constantly gagging. I had all sorts of tests, including an MRI scan, to check out what might be the cause. Eventually it was concluded that the problem was caused by a virus. It took about 2 years for the problem to gradually improve. My sense of smell is still not great but nothing like the above.
If you find that this applies to all sorts of smells rather than just instant coffee, I would suggest you go to your GP. I have just stuck my nose into a jar of M&S cafe noir instant and it smells ok. But perhaps the brands you mentioned have changed something in their processing.