I'm sitting here with 4-5 people and we have been fishing eels for 2 days now. Most of us above 2k in bait. At this point i'm starting to wonder if the droprate is bugged.
Um, the keys from fishing and mining are a 100% guaranteed drop if you don't already have one after 50 successful catches/ores. I would imagine you already got this key and either used or destroyed it somehow.
Talk to Zanik at base camp about Into the Forge and/or wait for next week's update (which should contain an addition I made that tells you which keys you have left to find).
Or try turning off you GOTE/porter if using them, as someone else suggested (though we have not seen any bugs that this is causing any issue, it can't hurt to try).