If you're selling an item/stack via the inventory by dragging it to the sell box down below, the price gets randomized every time. This only happens when you got the marketable trait and it only applies to crafted items that were crafted after you got the trait. If you're selling by multiselect instead, the price will still randomize every time after you dragged the item/stack inside the inventory.
I thought maybe dragging the item causes the game to shred it's metadata and it's treated like a new item instead. But that can't be it, because if it's a painting, the name you gave it remains intact.
So, I guess the reward trait applies a random multiplicator to boost the value, but that random multiplicator itself isn't saved anywhere. Though, the total value of the item (after applying the mult) is saved and even stays the same after a relaunch. But if for some reason the total value needs to be re-evaluated, you get a new random mult. Dragging the item causes that re-evaluation. In that case the bug has always been in the game and should be easily fixable by saving the generated mult from marketable, or just make it a constant value like 1.25 instead of a random one.
I've confirmed this in a fresh save in an unmodded game (v1.119.109.1020). It happens with paintings, nectar, sculptures from the woodworking table, probably more. No matter your skill level. It does not happen with flower arrangements, gemstones or jewelry.
