When I worked at an ML hedge fund 6 years ago, t-SNE performed the best and momentum was the feature that best predicted stock movements.
The actual algorithms for predicting price movement were fairly simplistic, most work was around strategies for dealing with overfitting and how to execute the trades. Accuracy was around 51-55% (a bit better than coin toss) so it was a big challenge to actually execute the trades and still make a profit after fees and other nonsense. Finding alpha is what ML is used for but that’s just the first step.
This makes intuitive sense to me, because the system you are modeling is wide open and you’re competing against others who have the same information. Achieving much more than 51% accuracy would be extraordinary. But if you get 51% consistently over time, with leverage, you can make a good amount of money.
My experience as well; seemed more accurate while prices were rising.