In the last update on 3/14/2018 in the patch notes this what was added:
-The fishing line thickness and its type has increased its influence on fish catch rate. As an example, chance of a strike when using thin fluorocarbon or monofilament line became much higher than when using thick braided line.
-Increased influence of the visibility of the components of the rig (the thickness and type of the line, the material and thickness of the leader, the size of the hook, etc.) of cautious fish, for example, such as Trout, Asp, Chub, Bream and Grayling.
So this means nothing was nerfed, you just need to change your set up to catch the cautious fish and to increase your catch rate on those type of fish.