I would like to first ask, how old is your specimen? This could be due to old age. Did you observe your mantis consuming it's own antennae as I would have a hard time accepting a mantis would do this. Sometimes broken antennae are just a case of aging as the animal becomes more fragile/frail. As for the "tip-toeing", I have a few Sphdromantis viridis that occasionally walk with one foot off the ground, eventually setting it down later. I certainly wouldn't worry about that.