I think gaining muscle is great and really important, but it's a glacially slow process compared with losing stored fat and water. So maybe our hard-earned new muscles won't show up so quickly on the scales, but they're still great for health and also burn more calories per day than fat does, which is a bonus. Also, I think it's normal for scale weight to rise and fall by 0.5Kg (or more) apparently randomly from day to day, and if you're getting slimmer and fitter that's way more important than random numbers on a scale. So well done :)