In one of my earlier posts, I discussed one of the reasons for compression failure and how we identified it using ETW traces and resolved it. Below are the list of other reason codes for your reference.

NO_ACCEPT_ENCODING The HTTP request did not contain the Accept-Encoding header
COMPRESSION_DISABLED No permissions for the IIS_WPG group or application pool identity on w3svc/filters/compression node in the IIS metabase file.
NO_COMPRESSION_10 The request is HTTP 1.0 and the IIS metabase key HcNoCompressionForHttp10 value = TRUE
NO_COMPRESSION_PROXY HTTP request contains a Via header which means the request is relayed via a proxy server AND the IIS metabase setting – HcNoCompressionForProxies has a value of TRUE
NO_MATCHING_SCHEME IIS could not find a matching configuration entry for the file extension of the requested web page. This typically means the extension was not added to HcFileExtensions or HcScriptFileExtensions list in IIS metabase.
UNKNOWN_ERROR Unknown reason.
NO_COMPRESSION_RANGE HTTP request contains a Range header and the IIS metabase setting – HcNoCompressionForRange is set to TRUE.
FILE_TOO_SMALL The file size is too small to be compressed.
FILE_ENCRYPTED The requested file is encrypted
COMPRESS_FILE_NOT_FOUND The compressed file was removed since it was compressed. This may also happen on the first request.
COMPRESS_FILE_STALE The compressed file has changed since it was compressed. It may be due to the symptoms described in Microsoft Knowledge Base article: 817442

For additional information, refer to this blog post from IIS support team.