I had the same problem with a half-link on KMC or SRAM chains. The half-link was fine initially with the KMC, but somehow got tighter [?] the more I rode, and began skipping. I switched to SRAM [+ new half-link] and it was fine for a while, but then the noise and skipping came back. I eventually switched ring/cog to different ratios and I'm not using the half-links at all anymore.