I'm not sure if this is a pest problem, grower problem, or no problem but a few of my Epis have this discoloration to them. It's not on any other succulent or near by plant, just these.

I received some of these cuttings last year and some this year.

It looks like it was exposed to a wet/cold environment and it gets that type of bruising as it tries to dry off. Or it could also be sunburn.

I'd check the root system just to make sure you haven't any rot.