I don't have any specific information from INZ and can't speak from experience, as this is a totally unprecedented event. But alleged breaches of visa conditions are investigated by INZ Compliance and I don't expect that the Compliance team are going to send Officers out in droves to check that people are working from home in the city that their visa states they are limited to. This is an entirely new situation which is covered by very little in the current Operational Manual or Immigration Act. Logic dictates that when the Government directive is that you are to work from home, then home is now your workplace until the Government directive says otherwise.