your switches may have configured by default Control Plane Policing and that could be rate limiting ICMP traffic.
see the following thread telling about autoCOPP and how to remove it.
note: instead of removing it you can increase the policing rate for ICMP traffic
Hope to help
local loopback: you mean within the same switch to a locally configured loopback address?
the loopback address may be separated by VRF's, you need to supply more config info to tackle this issue.
you can try to ping while specify source address in the same vrf