Hi..
I am using now Kdenlive 18.12.1b AppImage version with the ubuntu 18.04 OS. I am facing a issue with the normalization and gain effects in audio correction settings.
Whenever i use these effects, clips audio goes to mute. If i remove these effects then it's ok. Another two effects (Mute & Volume Keyframable) of audio correction are working fine. What should i do for solve this issue. Please suggest me.

I tested the 4 audio correction effects under 18.12.1b and they work as expected.

When you apply normalize does the track icon switch to mute?

What you can try: hit CTR+SHIFT+, (comma) and try/switch under playback SDL or RtAudio.

If that not help run the Appimage from the terminal (press CTRL + ALT + T). Move to the AppImage folder and run the .AppImage: ./Kdenlive*.AppImage
Do you get some error massage?