It'll be damage from last winter - thousands of cordylines either died, were damaged and gradually died, or if the owners were lucky, sprouted new growth at the base, which meant they had to chop the trunk right down to the ground.

Thanks Bamboo, do you think it will recover? Anything we can do? The leaves are still very green at the top but there are a number of brown leaves hanging down---looks like a Hawaiian grass skirt!!!

The brown leaves hanging down are normal - these will drop on their own, or you can attempt to pull or knock them off, or cut them if you can reach. I have to say it doesn't sound good - if the trunk is splitting and swelling, something's going on, so you'll just have to wait and see how it fares, I'm afraid. I'd certainly leave it in over this winter and review its condition next spring,

I'd just leave it be and simply 'suck it and see'. We in Gloucestershire, alongside many, had our toughest winter that any of our plants (bar a few trees) had ever known. It's little wonder that even a 'hardy' tropical specimen such as your cordyline suffered too. But like bamboo said many around my area have a contigency plan should the main stem be terminally damaged - they sprout shoots from lower down on the trunk - and this is what yours may well be doing to resurrect itself