Do you know if there have been some sucking insects around? There is a type of stink bug that gets on my cacti and they cause damage that appears much like what I see in the photo. They fly and are good at hiding, so it pays to be watchful. They were a new pest for me about 3 years ago, but I learned to keep an eye out for them. They first year they hatched many nymphs and did a lot of damage to plants they selected. In subsequent years I've not had as much damage because I've been more watchful and they haven't reproduced in the same numbers. All I've used is insecticidal soap for control. I've used it as a contact spray. Where they puncture the skin, it may allow an entry point for other pathogens.
