Integrated socket.io instance fails to upgrade to websockets (falls back to polling)

[EvilEls]

When using the integrated socket.io instance connections fail to upgrade to websockets falling back to polling.

This screen is taken from vis-2 adapter using integrated sockets. Request to upgrade connection fails and polling starts.

This screen shows vis-2 using separate socket.io adapter (at port 8084). Connection upgrade works. No polling.

Forcing websockets in web adapter makes vis-2 fail to load. It

Expected behavior
The internal socket instance should be able to use websockets, not falling back to polling.

Versions:
Version 7.0.9 in /opt/iobroker/node_modules/iobroker.web, node: v20.19.0, js-controller: 7.0.6 Ubuntu 20.04.6 LTS