@mouson @youshtec
Do you have AllowCorsFrom setting set for cross-origin requests: https://docs.mattermost.com/administration/config-settings.html#enable-cross-origin-requests-from
If you're using multiple domains, you should add all the alternative domains to AllowCorsFrom setting after which the websockets would work. Otherwise you'll get websocket connect err: websocket: origin not allowed errors.
Let us know if the issue keeps persisting