Entity tags (ETags) are a mechanism to check for a newer version of a cached file.

Problem may caused by Etag:

1. When using server farm, it may cause lower cache rate for different server generate different etag

2. Server need to check last modified time & etag to validate one file

By removing the ETag header, you disable caches and browsers from being able to validate files, so they are forced to rely on your Cache-Control and Expires header. Basically you can remove If-Modified-Since and If-None-Match requests and their 304 Not Modified Responses.

If you can access httpd.conf, you can add

FileETag None

Or if you can access .htaccess only, you can add

Header unset ETag

FileETag None

If you use both Last-Modified and Etag before, it will cause all cache reload after you remove etag