I was the one that mentioned this on twitter (sorry, a bit late other things to do...)
I got this while browsing at work. I know that this traverses a proxy and has some dns magic to secure the wifi (I'm on a wifi meant for externally trusted devices (phones, Bring your own devices etc.).
In firefox I see a continuous 403 on the https://forum.duet3d.com/socket.io/?EIO=3&transport=polling&t=MN8TA7g
So the socket.io doesn't seem to work.
On Chrome I get the settimeout handler violations and I don't see any socket.io connections, so it seems to regress to another means of communication.
I haven't had time to test this at home (renovating at the moment).
Chrome, latest version 69.0.3497.81 (Officiƫle build) beta (64-bits) on mac latest version 10.13.6
Firefox, latest version 62.0, all extensions turned of for the forum.