Can you say root bound?
This has such an easy fix. Divide and repot.
I like to spread a tarp, plastic tablecloth or old sheet where I'm going to work preferably on a waist high table. With a serrated knife, either divide into smaller plants or cut away the old and/or dead parts. Also, cut away the bottom 1/3 (or more) of the rootball. Now, you're ready to repot your plant with fresh potting soil and possibly plant a few more pots with the extra material. Empty everything left on your tarp into your compost bin and enjoy your not-so-new planting.