The cas16 are SkHynix, same as the Corsair lpx, which to date have had more issues with Ryzen than anyone. (RipJaws IV and V series) The cas14 are Samsung B-die, which are to date the most effective with hitting 3200mhz.(Trident-Z, RipJaws V and FlareX). The sk's will usually get 2666 or if lucky top out at 2933.
Of course Amd in partnership with its vendors keep coming up with some fixes, Gigabyte being a leading contender and this is solving many issues, but last I heard there were still some bugs.