Just wanted to post this in case someone experienced unable to be fishing during festivals like I did! Hopefully it may help someone out. I played on version 1.6.8
Possible solution I found by accident: spam buttons during ice festival minigame, leave while countdown is still ongoing and end the festival early, try using tools (farmer should be doing fishing animation with a plain fishing rod), dont save and return to title, start the day again.
Fishing outside of festivals was fine for me, but fishing during festivals wasn't working at all: I was unable to fish in the fishing mini game in the fall festival and during the festival of ice. When the countdown began for the mini game in the festival of ice, I tried many inputs to see if it would work. When I saw it wouldn't work, I just left the festival during the minigame. I wanted to replace a scarecrow with a rarecrow before the day ended, but found that I was just constantly doing the fishing animation. All of my tool animations were replaced by the fishing animation in the festival (the fishing rod was plain). I restarted the day out of curiosity and found that I was suddenly able to fish during the ice festival. It worked even after I closed the app and started up the game once again.