Yellow spots have appeared on my very healthy looking Christmas cactus. I transplanted it, cut off the leaves that looked bad and sprayed it with houseplant insect spray. It's not looking any better but I can't see any bugs.
Christmas Cactus Disease
Certified GKH Gardening Expert
These little guys are Epiphytes... meaning they seed off of other trees' bark. When you re-pot, make sure to use orchid planting mixes, as they are very similar in the way they grow.The next thing I would look into is the pH of the planting media. dolomitic lime will help with the pH of the soil. Here is another article that will help: https://www.gardeningknowhow.com/ornamental/cacti-succulents/christmas-cactus/advice-for-christmas-cactus-care.htm