Have to agree with @Conort2,cpds are of very poor quality these days and I won't keep them anymore because of this.I kept cpd’s in the past and had similar issues. I believe the stock available now is pretty inbred and generally of really poor quality. All other fish I kept with them were fine but I lost cpd’s one by one to stuff like wasting away, crooked spines, ulcers. I have a feeling a lot of them in the trade have fish tb or something similar.
You find the same with dwarf gouramis, neon tetras, guppy’s etc. A lot of the stock these days is of terrible quality.