Just a small update, I did some test and most of the time it only works on the next reboot after that it will come back to the same problem , need a manual restart of webproxy.
As in this post :https://community.ipfire.org/t/proxy-problem-after-upgrade-to-core-155-the-proxy-server-is-refusing-connections/5020/13 it had been report-it, I will just wait for a fix.
In the meanwhile i will check what i can do and find.
Thanks for the good help