Xeon skx, clx microcode causing inconsistent behaviour

Intel Xeon 2n-skx, 3n-skx and 2n-clx testbeds behaviour and performance
became inconsistent following the upgrade to the latest Ubuntu 18.04 LTS
kernel version (4.15.0-72-generic) and associated microcode versions
(skx: 0x2000064, clx: 0x500002c). VPP as well as DPDK L3fwd applications
are affected. The issue has been reproduced on other SuperMicro and
Cisco UCS motherboards outside of FD.io labs.