Chromebook zoom web client not working through proxy

[miyamiya]

Error codes: N/A
Device type: Chromebook
Zoom version: web client
Details about troubleshooting steps you have already taken
-windows/chrome/web client works as expected
-chromebook with no proxy works as expected
-chromebook App works as expected

when using web client on a chromebook, through a proxy server, we get
"Joining Meeting Timeout or Browser restriction" error and fail to connect.

using the same proxy but with Windows/Chrome/web client, things work as expected.

taking tcp packets, we noticed zoom web client (Chromebook/chrome) has a unique behavior when a proxy server is used.
-dns queries for "zoomxxxx.xxxx.zoom.us" (*guessing host is websocket connections)
-no requests happen for either above IP address
-no requests happen for above host names through proxy

the rest of the requests to zoom behave as expected with no dns queries and all going through the http proxy.

to confirm, i have done the same test through windows/chrome/zoom webclient, and all requests occur as expected, with no dns queries and all going through the http proxy.

any ideas on what could be happening?
much appreciated.