Popping in to say Ethan's advice saved me hours of headache. I've fought with the native URLSession and WebSocketTask APIs for about eight months, and used it across our fleet. Out of nowhere, socket connections would make no progress, and just retry every ten seconds. The instructions for debugging CFNetwork were of no use, and I had nearly no logs from CFNetwork explaining what was going on. Setting the debugging environment variable did nothing, the task just wouldn't budge. It's on brand with the overall experience of the Network framework, unfortunately. I switched over to WebSocketKit and have been beyond pleased. It has a very simple API and makes it very easy to migrate your URLSession code to it, usually with far less code being needed.

I contacted Apple Support and was escalated to a senior Mac advisor. I showed him this thread, and his immediate response was that because it is not reproduced with the Apple Multiport Adapter, it is a third-party issue. I insisted, and explained thoroughly, that this is an issue that was introduced by an Apple update, is caused by Apple's GPU drivers, and it's unacceptable that the solution to a botched update is that I buy a 3-port $69.99 adapter. I was told that they don't control third parties, "things change", and they don't control their drivers. Frankly, Apple has a responsibility to make sure they don't introduce updates that make previously functional accessories crash our computers. I was told that unless I can present a convincing argument, the case will be closed because it is only affecting third-party adapters. I explained that if the case is closed I will dedicate however long is needed to reverse-engineer the drivers and diagnose the issue, and come back with a solid case. They then promptly collected diagnostics and had me reproduce the crash three times (which happened one after another), and escalated the case to engineers out of generosity. While this has been escalated to engineers, I don't have high hopes that this will be fixed for us. If the sentiment that was shown to me is shared by the rest of Apple, the solution is going to be that we need to buy their multiport adapter and accept it. Completely unprofessional, and certainly not a way to keep me on as a customer.