It’s not that bad. There is a tool called Punch In that can customize the inserted sound based on the “hole” or selection you make, plus configuration instructions.
https://forum.audacityteam.org/t/punch-copy-paste/28906/1
However. Can I predict the past? You created an Audiobook chapter that had total dead silence between sentences and ACX Check didn’t like that.
Did I hit it?
You actually have two problems. ACX doesn’t like voice channels that artificially cut to silence between words or sentences and they really don’t like multiple effects piled on top of each other. The goal is someone telling you a story over cups of tea, not produced to death in an effects factory.
While technically, it is possible to “clean up” a chapter like that, it might take months to get everything to sound right—and that’s the first chapter.
Let us know.
Koz