No, the problem is that, in general, the more lines of code you have, the worse your program is. Perhaps people working at home feel less pressure to just code, and are thinking more about the problem and writing less code to solve the same problems - a massive win in productivity, which would appear as a loss by your measure.

On the other hand, perhaps people are indeed writing the same old code that they always were, just writing less of it.

So lines of code are not a good metric. Average number of features/user stories/tasks delivered may be a decent metric (at the group level, not for individual developers), as long as it doesn't become a target. Delivery VS estimate could also be OK, in the same way.