When you switch your client and working with the same employer, you do not need to file for amendment, but just ta new lca with new client will work. Even when you go for stamping, take the new lca, as the consulate might ask you where you are working and if you have the lca. If you go with right documents you should be find on stamping.

And i havent heard H1b denied based on the info you provided. It might have been some case about the specialty occupation.

Hope this helps.