Does not work with modded rods, just vanilla.

Yeah, I'm having the same issue on 1.16. It looks like the only thing that may cause the issue is isHoldingFishingRod() check, but the source code clearly shows that it is a type of net.minecraft.item.FishingRodItem.

After some experimenting, I found out that it is a catch detection issue. After forcing multiplayer detection, it works perfectly. @MrTroot Can you update the documentation to inform users to try out force multiplayer detection if it's not workign with modded rods.

The multiplayer detection setting is the current workaround to get this working with modded rods. I believe newer versions signify that the checkbox is intended for mod compatibility.