According to https://tools.ietf.org/html/rfc7232#section-2.1
> Likewise, a validator is weak if it is shared by two or more
representations of a given resource at the same time, unless those
representations have identical representation data.  For example, if
the origin server sends the same validator for a representation with
a gzip content coding applied as it does for a representation with no
content coding, then that validator is weak.

Therefore, after gzip, we should change the original etag to weak etag.