No wait, correction, I do see some improvement! I now realize that the strange behavior almost disappeared after removing the plant and a 50% water change. And at some rare moments I caught one eating but they remained almost totally inactive which was discouraging me. But after another water change I see several of them eating! I also noticed this black line along their body, so I guess that even though they didn't move a lot they still ate. Perhaps I was giving up hope to soon. It is quite cold at the moment so that will make probably them more inactive as well.
They are still not looking like extremely happy shrimp, but maybe we are getting somewhere. I will continue to do some more water changes.to get some more improvement hopefully
I also realized later that I had done some trimming on the roots, so that could have caused leaking of toxins in the water