I am experiencing the reverse problem.
I have a timeline with two sequential audio clips on it. I can fade the audio on the first clip with no problem. But Shotcut ignores my audio fade for the second clip. (I made sure to select the second clip before trying to apply the audio fade to it.)
The first clip shows the gray wedge and the audio fades. The second clip does not show the gray wedge and the audio does not fade.
I have tried removing the applied filter and reapplying it. I have tried changing the duration of the fade. Nothing has any effect.
This is the first time I’ve encountered this.
I noticed there is a post from Jan 2017 describing the same problem. Fade Audio/Video Filters Work Intermittently (17.01.02)
As suggested there, I tried manually fading the audio. The gray wedge appeared, but the audio still did not fade. (I used 5 second fade to be sure it was evident if it was working. I also used the peak meter for visual verification,)
My project is in limbo unless and until I can figure out how to make this happen.
Looks like a bug.