my giant frilly mushroom has been doing that since JH gave him to me. only half of him will attach and for a while the other half was twisted 360 degrees like a pretzel. he still hasn't split and it has been about 2 months.
It looks like its just detaching from the rock. Just like Leslie, I've had mushrooms that would only half attach no matter how long they were left alone. You're just going to have to wait and see.