You can manually calculate your High WaterMark by doing the calculation below:
High WaterMark = Highest Account Balance (Open and Closed Trades)
Example: You are on a Challenge with $150,000 and you have an open trade that reaches +$2,000 profit but you don't close it, and now it fell to +$500. Despite the fact that your new balance is $150,500, your High WaterMark will be $152,000 because your demo account had touched that amount at some point with that open trade.