I haven't encountered any problems nor am I reading about any (other than trying to make 64gb, 4x16gb kits run above 3200mhz)
In the X570 I :
My R5 3600 runs 2x8gb B-die kits at 3600 C14 no problem at all
My 3700x runs the same kit at 3800 C16 1:1 (1900mhz on the IF is about the limit atm, after that you are using dividers and need silly speed 4500+ kits to get the same performance as a well tuned 3600 kit running 1:1 IF)
I can run 3600 C14 in a Gigabyte B450 I (F41a bios) who's previous best "pre" Ryzen 3xxx was 2933 C12 while it housed a 2400g APU.
On Ryzen 3xxx 3600 is pretty much guaranteed, after that you are playing the lottery with how good the IMC is on the CPU you get !!!
3, 2x8gb kits of B-die tested, two sets of 3600 C16 and one set of 4000 C18
No difference between any of them
You can even pull 3600 C16 from cheap Micron E-die kits such as Ballistix Sport LT
You absolutely do not have to have B-die kits, the performance gains are minimal 
