I was having that issue when I was transforming him in bot mode incorrectly. It's really not documented well in the instructions, but I was trying to wrap one of the two insect legs per side, inside his torso going to bot mode. The correct way (I think) is to have both legs flat and on the outside of his back. Forcing one of the legs inside was putting pressure inside the chest cavity which was somehow effecting the head joint. Mine became noticeably looser and wobbly which disappeared once I swapped the insect leg position. Hope that helps.