So far, I've noticed this with two fish, the wolf eel and the angler fish. The Sim is fishing and I can see her catch the fish. Then she resets and the fish disappears. It does not show up in her inventory, nor does she get credit for catching it. It happened with the angler fish in the Sylvan Glade pond and the wolf eel in the area behind the Willow Creek Library. About a week ago, in a different save, I had no problems but I first noticed it in that save a couple of days ago. I started a new game and it's still happening.
I play without mods and I've repaired the game and deleted cache files. No luck. It's kind of hard to test and duplicate since those two fish are rare and not easy to catch. I guess my next step is to do a factory re-set and cheat fishing skill so I can see if the problem persists. Has anyone else had this problem?