Initial analysis of the issue shows that some objects on Ebay.com are improperly compressed and Sophos has an issue uncompressing these objects. Sophos has been contacted about this issue and they plan on including a fix for this issue in the 3.16 update at the beginning of February.
Until then here are a few workarounds:
1. Do no scan traffic from Ebay. com using the following policy:
2. Change AV vendors from Sophos to McAfee or Kaspersky.
3. In the ProxyAV management console go to Antivirus->Scanning Behavior and change the "decode/decompress error" to serve.