Playing the web build, the shop is broken. I got into a state where if I tried to sell a fish nothing happened. I tried refreshing (the last time I did that when the store broke it reset my progress back around 20-30 minutes, but better than a broken store). This time it restored to basically where I refreshed, and the store is still broken, but this time I can get gold by selling, but the fish don't leave the inventory. I also can't buy any upgrades - it takes the money, but doesn't upgrade.
I'm not sure, but it might be related to a full inventory - both times the store broke, I had 16 different items (15 fish, plus some gold) in my inventory (I know there's more spaces in the inventory, but it seems odd that it seems to have topped out at 16 both times - maybe there's only 15 different fish in the pond?).
So I think now I'm stuck unless I reset progress and start over, and the early game is waaaaay to slow to do that.