Isard-squid sometimes fails to start correctly

Some times fails to start as the spice viewers just don't work and even isard-portal is unable to reach the 8080 port to check it:

[WARNING] 269/162339 (13) : Server be_isard-squid/squid was DOWN and now enters maintenance (DNS NX status).
[WARNING] 269/162359 (13) : be_isard-squid/squid changed its IP from (none) to 172.18.255.19 by mydns/dns1.
[WARNING] 269/162359 (13) : Server be_isard-squid/squid ('isard-squid') is UP/READY (resolves again).
[WARNING] 269/162359 (13) : Server be_isard-squid/squid administratively READY thanks to valid DNS answer.
[WARNING] 269/162401 (13) : Server be_isard-squid/squid is DOWN, reason: Layer4 connection problem, info: "Connection refused", check duration: 0ms. 0 active and 0 backup servers left. 0 sessions active, 0 requeued, 0 remaining in queue.

To me it seems a problem with ipv6 inside this isard-squid container, that sometimes squid starts in IPv6 and others in IPv4. Forcing IPv4 in squid does not seem an easy option.