After having this issue on my own system and reading through several threads like this, I have linked this issue on my own system to the "Do not scan files larger than X MB" option in the web filter.
It seems if this setting is set excessively high, it will cause issues. This is just a casual observation I've noted from fiddling with it, this isn't based on any knowledge of the actual function of the web filter.
Problems seem to start happening if you set it higher than around 30 MB.
I think the problem might be related to connections timing out while the AV scanning is occurring.
Does anyone have any more experience with this or are you aware of any maximums regarding this value for the maximum file size scanned?
OP, please first try turning off web filter all together and see if traffic passes.
If this fixes the issue, try experimenting with the max file size scanned, starting somewhere real low like 8MB. Make sure you actually reset the web filter by turning it off and then back on between all your changes. You need to make sure the HTTP proxy actually restarts.
