Disable the pulseaudio module module-rescue-streams by sudo editing the file /etc/pulse/default.pa and commenting it out.
### Automatically move streams to the default sink if the sink they are### connected to dies, similar for sources# I commented this out to stop it defaulting to a 'dummy output' after sleep/suspend [JM:november 2019]# load-module module-rescue-streamsI'm guessing that there has been a change in the wake sequence such that, now, this runs before all the sound sinks are restored. Consequently, it decides all the 'dead' sinks need to be "rescued" to a new default/dummy sink. They all subsequently wake up, but they've already been rerouted to the dummy.
I'm also guessing that this could break some ability to unplug and replug speakers/headphones as and whenever you like, but I haven't discovered that for myself yet.