Track Changes Feature Not Working When Enabled

I recently received the 2017 version of FrameMaker and am trying to use the Track Changes feature. It allows me to turn it on and it works. However, as soon as I save a chapter in the book, the "Enable" button is still grayed out as if it is enabled but it no longer works for any chapter. I have tried saving and closing the chapter and saving and closing the entire book and the "Enable" button is still grayed out but the Track Changes isn't working.