Reproduced on 5.2.5f1, 5.3.5p2, 5.4.0b21. Works fine on Windows Standalone.

Repro steps:
1. open project "WWW_WSA.zip".
2. play the main scene in the editor. Press button "tap to run". Observe the console for the HEADER message.
3. build to WSA 8.1 or WSA Universal 10.
4. Press button "tap to run". Observe the output for the HEADER message.

Comparing editor and WSA build outputs, WSA build is missing "STATUS=HTTP/1.1 200 OK".

Log Should start like this:
Header:
STATUS=HTTP/1.1 200 OK
SERVER=Apache/2.2.22 (Debian)
[...]

but instead getting this:

Header:
SERVER=Apache/2.2.22 (Debian)
[...]