Sorry for my mistake.
I tried with rocky and stein and bot have same issue. 
After a live migration ping starts to work after some minutes (3 or 4 minutes).
I never seen this issue before. 
Ignazio

Il Lun 27 Apr 2020, 20:02 Ignazio Cassano <ignaziocassano@gmail.com> ha scritto:
Hello and thanks for you answer , I tried to enable post copy live migration on compute node, restarted the nova compute service
on compute nodes but when I try to live migrate a vm I have the same issue: I loose a lot of packets.
If I try with an instance which have a daemon which ping the default gateway, the live migration works fine and I do not loose packets.
I think this is a big issue.
I tried with rocky and queens with iptables_hybrid and both have the issue.
:-(
Ignazio