Using Studio plus 9.5 in windows 10.

Sound works ok when previewing files and placing them  on timeline but when I add a transition I get popup and no sound:
"Pinnacle studio plus 9 can not initialize audio playback.
The audio subsystem may be in use by another application"

Do you have the activation keys unlocked for some of those features

Pinnacle Studio 9 won't work well on Windows 10 or 11. Try using the free trial version of PS26 to see if that helps you.

https://www.pinnaclesys.com/en/products/studio/ultimate/ 

Everything is unlocked, everything works including sound until I add a basic transition then sound gone but when I finish and save the work, sound is there.

As Ramon says, 9.5 doesn't work well on W10 or 11 - it was writen 18 years ago! Has it just started doing this and worked correctly in the past?