My syngorium leaves remain curled. Very few open up, yet, I have new growth.
Do Syngoriums Need Large Pots
Certified GKH Gardening Expert
These plants are normally ok a bit rootbound, so that is likely not the cause of your issues.
I would recommend checking the plants for pests, making sure the plant is getting enough light and water and that there are no diseases. The leaves can stay curled if the plant is stressed, but there are many things that can stress a plant. The ones I listed above are the most common stressors.