I am leaning towards J.C.'s explanation. I also see damage spreading to some of the surrounding offsets.
Is it in full sun? If so, move it to bright shade.
I also agree about making sure your potting mix is very fast draining. If it has rained you would not need to water them.
If the discolored rosettes are feeling like they are beginning to rot I would remove them. Also check the soil and see if it wet.
