Gmail cannot view picture through web browser through squid proxy server

Hi, forum reader, I have a squid problem. We have 2 squid proxy for two different group staffs, both of them can access gmail for web email access. It used about half year. One day we send out email with image but one proxy group user cannot view that pic but another group can see. Any idea for happened on the proxy server? how to check and fix it?

Thanks for your help

iPhoneTapatalk

Did you clear the caches on your proxy server first, as part of the debug process?

Yes, cache had already been cleared.