DisplayPort/HDMI audio gets stuck very quickly

On Qubes 4.0 audio via DisplayPort was working fine for me. On Qubes 4.1 I cannot get it to work. Sound output works fine on the internal speakers, but when setting dom0’s PulseAudio to play on DisplayPort (it calls it HDMI, but that’s normal) there’s no sound coming out and the bar showing the current output level doesn’t show anything.

To track down the problem I turned off both sound cards in pavucontrol. Then I tried playing audio using aplay directly on the sound cards from dom0. It works fine on the internal speakers, but when playing on the DisplayPort I can hear the first few hundred ms of sound, then the sound stops and aplay hangs indefinitely.

Neither dmesg nor journalctl show any related error messages. Same happens when trying a different monitor with a different cable.

Any ideas how I could debug this further?