Most likely the buds were still a little too moist when you put them into the tub. When they hang dry, the buds will start to feel crispy on the outside. When you out them into a closed tub, the moisture within the buds redistributes and they will feel “soft“ the next day. When the moisture content is perfect, this wont happen anymore. Do you have any sort of meter/gauge for humidity? If so, this could help to confirm. There are little devices that will fit inside a jar or tub (made for cigar humidors) that work well for this. Be wary of mold.