Seems to be a configuration error on the server hosting the viewer app. In the browser console, there’s an error during connection:
Refused to connect to ‚ws://192.168.1.204:28252/‘ because it violates the following Content Security Policy directive: „default-src ’self‘ ‚unsafe-inline‘ https:“. Note that ‚connect-src‘ was not explicitly set, so ‚default-src‘ is used as a fallback
Happens in different browsers all the same.
Dirty workaround is to save the viewer page to the local hard drive and load it from there. Incorrect CSP is not applied then, and it works, although with some minor glitches.