Can you send a picture of in situ and another of the leaf that are curling, there are several insects thaqt lay eggs on the leaf then set about curling the leaves into a tube like shape to protect the eggs/ grubs from predators like birds, ants or other insects that feed on eggs / grubs.
Or it could be as simple as the wrong conditions they are growing in,
Have you watered the plant enough, I always use rain water as the tap water is not acidic enough for these plants, they also like to be fed every few weeks in the growing season when still young, they also prefer a slightly acidic soil. Maybe a soil test kit from the garden store (they are not expensive just a couple of dollars) that kit will tell you IF you need to amend the growing conditions in the soil but also, can you open out one of the curled leaves to see IF there is any insects inside, they dont bit, they dont fly and they wont harm you in any way, but it might just help you identify the problem.
IF no insect found then, look at the growing conditions and change what's wrong with that.
Here are some pictures. It's going quick. I water at least once a day. Don't see any signs of bugs. It's got to be something in the soil. The plants have been there about 18 months. There were 3 side by side. The smallest is aleady gone. This is the largest and it is going fast. The one next to this is next.
Go to the garden store and ask for a liquid fertiliser for Acidic plants like your Gardenia, Azalea's ect, they are prefer acidic soil and IF you have planted them in the wrong type of soil then the symptoms you show in the picture can be the problem of yellowing leaves, dropping leaves and some other symptoms.
The middle picture is the most clear and I don't see the curled leaves you worried about, and now that you have produced the pictures and I've looked them over, I would say the problem is the growing conditions being unsuitable for these plants, I would go to the garden store for a very cheap soil testing kit and do a test on the soil at the root area of the plants and a few areas around the bed as PH can fluctuate in the same garden and bed, the test will tell you what is required to amend the soil to suit. The plants have to have a peat based soil with added horticultural sand or or sharp grit as this will allow the type of drainage needed BUT the peat helps with the acidic needs of the plants.
Hope this helps a bit to remedy the plants needs.
Best regards WeeNel.