Need Help with the Wash Sale Rule

If you day trade actively one stock and your cost basis runs into millions but profit is low (let's say for example 10K), what would the tax implication be? Will the tax still be only on the profit of 10K? I ask because sometime ago, there was a news of a RobinHood trader incurring a tax bill of $800K with the Wash Sale Rule even though his profit was only 100K for the year.