I add a product to the cart. click keep shopping. add a second product. one of 2 things happen: 1. First product removed from cart. 2. I get two of the newly added product. I’ve tried on a Mac in Safari, Firefox and Chrome. Then switched to a PC… same nonsense. Look into it.
You should contact Envato Support and let them know about that.
It’s definitely a weird issue that I couldn’t replicate myself, but I’m sure someone from support can look into it.