Got S2 scales after my original set died after five years.
Firstly, the new set had me much heavier.
Secondly, the variance in weight from day to day is ridiculous.
What is going on?!?!!

variance in weight from day to day is ridiculous.
I don't see anything extreme here. I weigh 66 kg, I always take the measurement in the morning before breakfast, and I can get a 2 kg difference in 24 hours just by taking in more or less food and/or water during the day. Oh, and I do not use a garmin scale, if you think that it's the index's fault.
Yes. Typically, after a long workout, the next morning my weight will go up as much as 2 kg. Just taking in more food and fluids that have yet to be fully processed by the body. Almost guaranteed to drop by the same amount and more during the next day or 2.