Allow me to use a cake analogy, because everyone loves cake....

Allow me to use a cake analogy, because everyone loves cake. They've managed to figure out which ingredients need to go into it, how long to bake it, and how to construct it layer by layer. That's what they're referring to when they say they've resolved the manufacturing issues. Despite having the process down, the cake doesn't taste quite right at the moment so they're tweaking a few of the ingredients to make it taste exactly how they need it to.