I have same issue here on macOS 27.0.1 (26A434). MacBook Pro 14" (2021), M1 Pro (MacBookPro18,3) Displays: Philips 27E1N2600A via HDMI audio works Philips 27E1N5900 via USB-C (DP Alt Mode) audio fails I also tried another USB-C display, and it fails the same way. Symptom: Playing to the USB-C display hangs for about 10 seconds and then fails. No samples are ever output. Built-in speakers and the HDMI display work normally. 100% reproducible. Log (matches the original report): HALS_IOContext_Legacy_Impl::IsTimeRunning_Helper: Device ... is not running. could not establish a timeline after waiting 10000000 microseconds stopping with error 1937010544 StartIOThread: the IO thread failed to start, Error: 1937010544 +1 for a fix.

The code I attached seems 404. I will attach the file again. radio_bug_swift.txt