I never saw anything like that but, a few things come to my mind.
Network: Are you accessing from a saturated network?
Disk: Is the ESXi installed in a USB or a disk with intensive use?
I suspected the network or putty to be the problem, but seeing the same result in DCUI as over the wire was a confirmation that the network is not the problem. ESXi is on an SD card and syslogs are redirected to a high performance LUN.
cpuidMask was carried over from an older version of the esxi. removing all cpuidMask values from /etc/vmware/config corrected the problem with esxtop