Cannot ping IPv4 address, but IPv6 ping works
I had a similar issue and got a positive response when using IPv6 (ping6) but not IPv4 (ping). I also had the symptoms described in the question Why will my Mac only load Google and Facebook?.
This problem started to appear after disconnecting from the VPN. So, after terminating the VPN service, networking began to work fine again.
sudo killall -9 vpnagentd ciscod