This is a fungus causing a leaf gall. It seem to be worse this year than usual. I have one susanqua that has had many of these. I suppose it is because we have had a cooler than usual spring and quite a bit of rain. The treatment is to prune off the affected limbs and discard them in trash (not the compost pile). Hope this helps.

When it rains a lot, the pH of the soil can temporarily be affected and cause some yellowing but curling or swelling might indicate a pest is causing that problem. Can you post a picture of the bush and several close ups of the affected leaves (top and bottom)? Pests can hide underneath the leaves and they sometimes come out of hiding at night so you need to identify them when they are out doing their damage.

I agree that leaf gall is the probably culprit. Very common during rainy Springs.

I agree - it sounds like Leaf Gall. Also check out the link below for photos.

Here is a link that might be useful: CamelliaWeb Gallery - Leaf Gall