Does anyone have any idea of what's causing this? I already sifted through the soil and repotted these guys a while back, but didn't spot anything suspicious. It almost looks like the center part is like raised/bumpy too, but I have no idea what that would be about?

Any help is appreciated, thanks!

It looks OK to me. It might need a thorough watering as the leaves don't look as plump as it should. I see a leaf or two sort of limp. Hopefully leaves will look better. Not sure why there would be holes/bites unless presence of bugs taking a bite here and there if plant is outside.

I had holes in some older leaves on a flapjack plant. I could only guess it was a fungus? Don't know though.

I am looking at your images and I am not seeing the vibrancy of their overall color. It looks muted or subdued. I think that a large part of your problem is insufficient light.
I would try introducing more light slowly. From where they are growing now, move them to more light. Take a picture. Leave them in the new spot for a month.
Check your image taken now with the one you take in a month in more light, see if it improves. If it looks a bit better, try more light. Repeat the imaging process. I only suggest images to assist you in evaluating their health. Sometimes we think they are doing better, or not, but by comparing images, you may have a better idea.
See if in 2-3 months from now, they don't look better.
Also try a bit more frequent waterings. Different succulents like different levels of watering. Maybe yours will respond to more light and more water. Because now I feel that they look a bit limp and dull.

Bill sounds right on. Not all succulents do well being too dry.

I killed a bunch of succulents when first starting out. I kept reading about how they had to dry out, but so many of them died. I've had much better results from watering much more often and using mostly clay pots.

Clay pots help in 2 ways. First, the soil can breathe through the clay, so the risk of roots rotting is drastically reduced. Roots need oxygen & moisture at the same time to function. Unless you're really trying, it's hard to overwater in a clay pot. Even I have not managed to accomplish this.

Second, they turn a lighter color as the soil dries. If you see that, you know it's time to water.