Then I'd say the probabilistic nature of the model was not represented correctly by the seller.

Saying the algorithm makes 95% winning trades may not mean much if those remaining 5% of trades cause you to lose most of your value.

Protip, do not try this argument in Vegas.

Good point, but at least the probabilities of casino games are generally known and available AFAIK. People just tend to not care or have a confidence bias.

If it's a robot, designed, programmed appropriately, and trained using the correct data to digest and understand later data, can it be unlucky?

John Maynard Keynes' remark that 'the market can remain irrational longer than you can remain solvent', springs immediately to mind.

Yes, unlucky just means that random/arbitrary decisions or events didn't "favour" you.