https://community.adobe.com/t5/audition/add-silence-dialog-box-stops-appearing/td-p/10688443?page=1

Happens on PC (me) and here on Mac. So cross platform. Happened to me when editing stereo and mono files working with wav, mp3 and m4a files.

Here is info from others:

When adding a chosen duration of silence to a recording, I go to: Finder > Edit > Insert > Silence. A pop-up dialog box then appears allowing me to choose the time duration. I then hit "OK", and away we go...

Currently, this operation will work two or three times before the final dialog box stops appearing, never to return until I restart my computer. I have tried simply quitting the app and restarting to no success.

This is obviously very annoying, and having not worked with many Creative Cloud Audition features long, I am not aware if disappearing pop-up dialog boxes is an app-wide issue.