When I first had custom molds for my KS6 they were uncomfortable. At that time I happened to go to a different Costco. They said they preferred a different mold supplier. They made new molds and they worked comfortably for many years.
Custom molds should not hurt. I have worn custom molds or aids for many years. The past few years I have tried living with tulip domes.
I finally visited a different Costco audiologist who had a little device that he could press in my ear to find out where it hurt, and polished the molds down more. That made them tolerable for a longer time but I returned them anyway shortly before the end of the 180 day return period, because they were still not really comfortable.
My hearing is still good enough that I function well without them, but if it gets bad enough that I can’t, then I’ll go back and get the latest model and try again.
Just remember that hearing loss can be a “use it or lose it” situation. Our brains get accustomed to not hearing certain freqs and can either fill in those lost freqs with tinnitus or we may lose the ability to hear some of those freqs in the future, even with hearing aids.