App (irium webcam ) changes default audio settings every startup
try with another way:
paste this in a file with a ".sh" extension inside /home/
#!/bin/bash
pactl set-default-sink **Your-Device-Name**
give the execution auth
chmod u+x /home/<yoursession>/<fileyoucreated>.sh
and fill the path textbox with these file location in the autostart config.
Remember deactivate this option when you want to not use those device anymore.