The write speeds?
" That may cause a problem for the memory write speeds when using processors equipped with single CCD - any Ryzen 3000-series with eight or fewer cores - because the data fabric-to-UMC speed, inside the cIOD, is 32 bytes for reads and writes: they don't match.
AMD says that this is a calculated design choice for Zen 2, due to most client workloads not writing as much. Halving the data link write speed between CCD and cIOD saves area, improves power, and has ancillary knock-on benefits, too. The downside is half-write speed because of the slowness of the data fabric in that direction."