Something weird, by chance I was experimenting recently with encoding 5.1 (via the ac3 template) and it worked OK, but after the upgrade from windows 10 (1803) to (1809) the output files are silent. I can still and hear 5.1 source files in Vegas 16 timeline.
I can also still play (in a player) the old .ac3 output file (and hear 5.1) made before the upgrade, so there is nothing wrong with my sound system.
Does anyone experience this issue as well?