Check the nickel thing again because a nickel is 5 grams but only if it's not worn down, and old nickels can be a bit light. The real issue is you need a weight that's close to what you actually use, because a scale can be fine at 5 grams and way off at 500. I test mine with a full 500ml water bottle since water is 500 grams on the nose, and that catches drift way better than a coin ever will. Five nickels stacked is only 25 grams, so your scale reading 31 there is a red flag, but it's also just a tiny load. Try weighing something heavy you already know, like a sealed 1 kilo bag of sugar, and see what it says.

Ha, America's Test Kitchen tested this and cold water with salt made zero difference in the final dish.

Your wifi probably wasn't the thermostat's fault.