When browsing through the Symantec Web Gateway proxy, some websites that are allowed by policy are only partially loading or load without any formatting.
The Custom Report page shows various URL's related to that website being allowed when this browsing is occurring, but there may be some Blocked traffic that is not immediately identifiable.
A Content Filtering category is being triggered with an action to "Block" the traffic. This may be seen either with the categories "Streaming Media", "Content Delivery Network" or "Social Media."
Please review the Content Filtering policy triggering the blocking action.
If it is the intention to allow, for example Facebook, however block all other "Streaming Media" and "Social Media" content, you will need to add a policy exception or whitelist those additional URLs. Using Facebook as an example, their Content Delivery Network is located on many URLs, such as the following:
Using this example as a guide, you should be able to determine other websites' Content Delivery URLs that are being blocked at the exact same timestamp that you loaded the intended website's URL.