The app changed my weight from 72,4 into 724 kg. Four incredibly tough rides later I checked my settings and discovered this bug.
Yeah, update your Companion app, this was a very real bug that was fixed a couple of months ago. Didn’t impact users with all-American locale settings which is why some might have not noticed.
A speed/power calculator I tried says that 200 W and 724 kg gives you about 17 km/h on a flat road so while it certainly is noticeable (“incredibly tough” as remarked in the original post) it’s nothing like 1 km/h. After all, most of the power goes into overcoming wind resistance, which is a function of surface area, not weight. Until you start going uphill, of course.