AST SpaceMobile was a stock darling in August, but not so far in September.In the run-up to AST SpaceMobile's (ASTS -0.65%) most important satellite launch to date, investors piled into the stock. Shares of the company soared 40.4% in August, according to data provided by S&P Global Market Intelligence. That came as the maker of satellites for space-based cellular broadband prepares for the launch of its first five commercial satellites as early as this week.But investors may have gotten ahead of themselves ...