I have had imbue weapon and have fought probably 1000 rounds with it both in an out of water. The offensive prog has never fired, it only heals. Am I just bad RNG or is this broken now? Previously I would get the offensive prog that would do the water damage spell. Recently it was changed, perhaps its broke now?

So I was able to make it happen really easily:

1) Be a ranger
2) Be a mariner
3) Fashionspear
4) Imbue the harpoon
5) Wield the harpoon
6) Fight a mob in the water

At that point it took under 20 rounds for a prog to fire.

You've done ALL those steps? Remember, when you do a bug post please be detailed - otherwise I end up wasting my time.