What I am seeing in your photos looks like rot to me, which makes me a minority opinion here. I would dig them up, remove the soil (without washing) and damaged leaves, let dry out of the sun a few days, then replant in a soil mix that does not use moisture control. I do have some problems with sunburn here when I move my plants from a semi-shade position to full sun but it does not look like what I see in the photos.
I think you need to dig a few of them up and take a closer look at the damaged leaves. If the leaves are "squishy" where they attach to the stem or have a squishy texture before they dry up, then the root cause is rot. I do strongly advise you to stop all watering for a few weeks, making sure that they are not exposed to hot, direct, afternoon sun. If you do find rot, then you need to air dry the plants out of the soil as quickly as possible. If it is rot, then it is likely the damage will increase unless you dry them.
