I have noticed that the CRAFT button isn't really "smart". I could have all the items needed but the button does not appear until i go into each item, and the go back to the main item i want to craft (via the mini navigation on the top -- i click on the items listed on top).
See attached image for an example where the CRAFT button does not appear clickable. I have to go into each (sub) item and then go 'up' for the craft button to appear.
I have also noticed that sometimes BATTLE button seems grayed out (i have enough energy, etc just the button was somehow gray-ed out) but they are still clickable. <-- discovered they were still clickable coz my fingers moved too fast and pressed on the button and realised... Hey, it's a bug!