Just used my Tanita scales and uploaded the results, to my surprise the modern Garmin site was showing a weight that was 1kg heavier than the weight on the watch. I switched to classic and it showed the correct weight.
The incorrect weight shown on the modern is the same weight as the last weigh in (only yesterday).
Incidentally, the new modern websites weight section has, what I consider, an awful view. Because the range for the graph goes from 60kg to 100kg, the fact that I've managed to lose 2kg this week has made little to no impact on the graphs line, leaving it virtually straight!