I filed https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=970687, where Quodlibet would segfault when playing any audio stream. On IRC #quodlibetm lazka helped me track down this bug, and we believe the QL issue is caused by this.
Could the upstream fix be backported, so QL can be used for audio streams on Bullseye again? Thanks, Tobias