Thank oneillpt for the extensive testing.
The missing text was my fault - I delete certain <p> tags in opf file with content inside.
All the recipes that were not working contain only one feed. It was not taken care before in my implementation.
Attached is the modified CalibreKindlegenHelper.py. Replace it with the one in azwplugin.zip. I'll do a further extensive testing soon and pack it in the plugin.