I've used these in the past, still have many in my assortment since it came with 48 coils.
I'm not sure about the SS316 coils, mine are the Kanthal, but they were DIRTY coils. I dry burned mine (not to cherry red), but pulsed them over and over until no residue came off of them. I probably pulsed them a little hotter than I normally do, but wanted any residue burned off. They seemed ok after that and I vape unflavored so I probably would have noticed any after taste.
If you didn't pulse them enough to help burn off any residue, that might be what you are experiencing. I was kind of surprised how many times I had to pulse them before they stopped producing visible residue.
Once I got them 'clean' and any hot spots out, they seemed to do fine for me. I usually replace my coils at about 4-6 week intervals, and these held up well for me.
For the price, maybe pick up the Coilology assortment in Ni80 or SS316. Can be had for under $15 and is a 42 coil assortment that is very clean in comparison.
Just think there are nicer coils out there for the money, but I will continue to use mine here/there until they are gone.