Not only zip file, but also large file can't be forwarded. There is obviously some rules applied on chrome, some of them is .php. I don't really know about all this rules. Its also check the availability through check.googlezip.net/connect or within the same persistent connection which is http/2. Doing all of that check would make a latency problem.
I propose to only forward most common compressible content.
@rule \Ahttp://.+/.+\.(?:jpe?g|gif|png)