Hi all, today I noticed some black bruises on a cutting I have had for a few months. I only noticed it because of a patch of white scar tissue on the side that faces the sun that I don’t remember seeing a few days ago. When I flipped it around, the back had a lot of scale insects and several black bruises, some of them seem to be turning white like the patch on the front side (first photo). I’ve spent the last hour scraping the scale off with tweezers. I don’t think it’s rot because I have never even had this pot anywhere near a drop of water in all the months that I have had it. We haven’t had any frost yet, either. Has anyone had scale insects cause damage like this? I hope it’s just damage and not a bacteria or something

Scales attach their mouth parts to the plant and sucks the life juices out of the plant.
They can leave marks, but not such large ones as seen in photo #1.
I see new growth on the top edge of the paddle.
Also, you said that you have never watered this plant.
I believe the white "desiccation" you are seeing is the natural drying of the plant.
The new growth had to take its energy from somewhere.
The new growth indicates that it is time to start watering your Opuntia.

Yes, the larger brown spot is probably due to sunburn or something else other than scale bugs. They will leave a small scar after they are removed, if they have been there a while... the size of the bug and not much more. I wouldn't be too worried about the brown spot in the picture. The plant will most likely grow out of it.