I don't know what is causing it, but what I would do if I were you would be to remove one non-essential ingredient at a time until the sour flavour goes. For example, in your base, you need water and onions -- all of the other ingredients are optional. In the main course, you need the oil, base, the chicken and the mix(ed) powder -- again, nothing else. If eliminating each in these does not identify the culprit, then you will need to repeat by eliminating one ingredient from your mix(ed) powder at a time ...
** Phil.