Chrome does not see Access-Control-Expose-Headers header

Question

I have a problem with Chrome - in the network tab it only displays an empty Access-Control-Exposed-Headers header.

In postman the header's value is visible:

When trying to access the ETag header through the getResponseHeader('ETag') method of the XMLHttpRequest I'm getting a Refused to get unsafe header "etag" error. I already ran out of ideas how to fix this. Does anybody know what could be wrong?

EDIT: Apparently that behaviour is caused by the Origin header - when it is present in the request, the Access-Control-Expose-Headers in the response is empty. Unfortunately, I don't have access to the backend code, so I can't provide an example. All response headers:

HTTP/1.1 200 OK
Server: openresty/1.9.7.5
Date: Sun, 03 Sep 2017 13:02:55 GMT
Content-Type: application/json; charset=utf-8
Transfer-Encoding: chunked
Connection: keep-alive
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
X-Content-Type-Options: nosniff
Access-Control-Allow-Origin: http://localhost:3000
Access-Control-Expose-Headers:
Access-Control-Allow-Methods: GET, POST, PUT, DELETE, OPTIONS
Access-Control-Allow-Headers: *,x-requested-with,Content-Type,If-Modified-Since,If-None-Match,latest_time
Access-Control-Max-Age: 1728000
ETag: "eef3e52bc505031d93da42098f32cc60"
Cache-Control: max-age=0, private, must-revalidate
X-Request-Id: eb5c7353-0b4b-43c8-b2ff-4763d56d9ec9
X-Runtime: 0.015680
Access-Control-Allow-Credentials: true
Vary: Origin