Sometimes I get the message "You caught something interesting!", but nothing shows up in my inventory (no shells, no painting, no nothing).
Last time I had an issue like a message not giving what was said (caught sos bottle while using a fishing net), it couldn't make a stack of a single only item in my inventory, could be it.
Or it could be the item simply doesn't exist.
Also, please, put a maximum of shells, painting and pillows in a chest and remove all the scrolls/iron weaponry. please.