Translucent spots on astro ribs?

[tasuccs]

I got what I thought was a very healthy looking astrophytum myriostigma at a local nursery a couple of weeks ago, and after a few days in bright shade put it in a spot that gets sun every day until about 2pm (my climate is similar to San Diego). I then noticed a tiny orangy-translucent mark on the edge of a rib that I figured I must have missed - I hadn't watered or done anything to it yet.

Today I sort of repotted it into a nicer pot almost the same size (didn't see any reason to switch out the granular soil it came in, the roots looked good and it was loose and bone dry a week after being watered) and I noticed the marks were multiplying and spreading (see backlit photos below).

The marks are subtle but distinct enough to be sure something is amiss and be concerned. If anyone has seen this and can tell me what I need to do, if anything - I'll be very grateful for help.