I have suffered from this issue for 2 weeks.
<Symptom>
Slow response or sometimes you can't access to Web pages when you use Symantec .cloud Web Security Serivce.
I realized this issue on November 14th 2016 and I called to Symantec but, this issue isn't fixed yet.
<Current environment>
Out current environment is as follows:
PC --> domestic proxy server ---> Symantec .cloud Web Security Serivce ---> Web pages
<Isolate the cause>
To isolate the cause, I've done following case of connection test.
1. Full path test
PC --> domestic proxy server ---> Symantec .cloud Web Security Serivce ---> Web pages
Result: slow
2. Except the domestic proxy server
PC ---> Symantec .cloud Web Security Serivce ---> Web pages
Result: slow
3. Direct access to Web pages
PC ---> Web pages
Result: fast
From these results, the point of failure is Symantec .cloud Web Security Serivce.
I hope fix it as soon as possible!