With a deep understanding of markets and trading I fail to see why you see 'luck' as an explanatory variable is inversely correlated with the frequency of your trades (notwithstanding the effect of trading expenses)?
From what I have gleaned the following seems to be true:
1. Your algorithms worked (made money)
2. Then your algorithms did not work, but you could not figure out why
If you do not know why something stopped working it seems unlikely that you had a full understanding of why it was working in the first place. Without understanding the nature of the predictive value of the algorithm while it was working, its success seems to be good fortune.
Your algorithm could have shown a systematic correlation to any number of factors that could have created strong performance over several months. Performance would then be attributed to accidentally 'timing' a favorable market.
I know you feel differently, what am I missing?
And either way - kudos on the $500k.