Whew, it's good to know it's not just me having problems with thread unfolders.
I've tried all the options on Userscripts.org in the vain hope that perhaps a different one, or reinstalling the one I had been using for ages, would work but no dice. Chrome must have changed something in their code somewhere. The link still shows up for me to unfold but the script itself doesn't work. Unfortunately, I doubt the available scripts are ever going to be updated since most haven't seemed to have been touched in over a year.