Simulator runs a stack for macOS. On iOS, without a parent view, you're foregoing the standard APIs that are otherwise needed and help complete the talk-thru necessary for your connection to complete.
And before you ask, I have no idea if those APIs could be sufficiently identified and added to a standalone iOS WKWebView implementation that would survive, etc. Even if they did, it would seem coals-to-newcastle, and much easier to just do it BTB in the first place.
Thanks. If I had reasonable assurance that it would work as long as it has a parent view, that would be fine. My concern was whether failure might occur when parent view was not visible or memory was tight.
My alternative is to ditch the node.js library, and talk to the server directly, using JSON-RPC over https or websocket. That doesn't look too bad for immediate needs.