Something odd going on with compile to Kindle

I have a couple of things to add/fix in my MS that I have previously uploaded to Kindle (a year ago). Basically it was the addition of a line or two of text in the Acknowlegement section at the end of the book. so I made the changes in Scrivener, compiled as before, uploaded to Amazon, checked what it would look like in theiir online previewer
and…whoops.

Under Table of Contents it is only showing Chapter One. And when I scroll through the book, I see that all of the Chapter/scenes are now put into one document (Chapter One), Scene breaks are there, with a couple of lines between scenes in a chapter. But at the end of the chapter there are a few lines and then “Chapter Two (or whatever chapter is next)” starts at the bottom of the page or wherever it might land. In other words not on a new page as it should.
I haven’t touched any of the compile settings from the last time I uploaded this successfully.
It looks like, as far as I can tell, that all of the section layouts are correct.

There is also no front matter or back matter, even though both those options were clicked in Compile. The cover is in there, though.

What’s going on? Why has this messed up my chapter settings/front matter/back matter? How can I fix this, as in compile it is showing everything set up as it should? Is there something odd going on with Amazon?

Also…when I uploaded the file to Kindle Previewer 3, to check it before uploading to Amazon, it all was fine. BUT I did get a message saying that new uploads or changes to previously published MS should be in EPUB format. I uploaded the file as a MOBI, so is that the problem? Is Amazon requiring EPUB instead of MOBI now?

Any help you can give is appreciated.

Just to update this…I called Amazon to see if they had any suggestions. As it turns out, they told me they now require ePub files, NOT MOBI.

Huh?

There has been zero communication about this to their authors. So weird.

I uploaded an ePub file, and it all was fine.