Privacy concerns ...about government being able to build a good picture of where you go, what you do.,
Misuse of that data could be to manipulate you, like those Facebook/Cambridge analytica scandal. Or to check that you are behaving in the way they want you too.
In an authoritarian state that could include noticing if you go to the same pub or church as a dissident, guilty by association, or you may be guilty of not contributing enough in some way. In nazi Germany, talking to a Jew who had been your friend and neighbour suddenly became traitorous.
But this data is already readily available to the government - through the triangulation of your mobile phone (have you ever watched Hunted?). The only new element is combining that data with information about suspected or confirmed coronavirus cases.