2 out of 15 IP addresses can't get to the internet. no error, no nothing.

Dear All,

I am deploying a pilot to implement SWG (proxy mode) on our network. after my individual tests went ok I decided to test with 15 users and everything went good for a week or so. then 2 users started to report problems accessing the web. there were no errors. the browser just sat there waiting for the web page to load.

those 2 IP addresses belong to the same subnet as the ones that work.

what did i do to try to understand the issue:

1. I can ping to those IPs from and to the admin gui. so, no network problem
2. I can "telnet SWG 8080" from those IPs and the proxy respond.
3. when I reproduce the problem on a virtual machine (it is definitely a problem with those particular IPs) the browser keeps trying to open a website and that last forever. I can see the browser trying and trying and in the end there is no error of any kind.
4. I tested those particular users from different IP and all worked ok
5. I changed those IPs to another on the same subnet. everything works
6. when I restart the SWG virtual appliance the problem dissapear temporary.

how can I debug this? there is no valuable logs in the GUI even after I set up a syslog server.

thank you in advance.