The indefinite "Please Wait..." Websocket issue seems to be triggered by VPN - any insights / mitigation?

Web apps hanging on the “Please wait…” message seem to have been occurring almost randomly, regardless of TOML settings (e.g. CORS, Websocket compression, etc).

After a week of investigation I believe I can track down the cause to connections over VPNs. Browser console messages reflect failed websocket connections. If the app is left open in this state eventually the browser will show “Error 60000”, whatever that means.

I realize that VPNs (corporate and private market commercial in nature) may involve some obscure settings that can’t be directly controlled by users or developers. This is problematic because the apps need to work under most normal circumstances and VPNs don’t normally cause web technologies to break so spectacularly.

Is there any existing knowledge or guesses at either how VPN might affect this?