Chapter Titles Don't Work/TOC ditto

I’ve saved each chapter to an individual file w/in my binder & when i go to compile, I have set separators by section break; unticked the “override title prefix separator” box, set my title prefix/suffix with Chapter <$t>…
and what I get when I compile is a TOC that lists the front matter but the TOC is just 1, 2, 3…; and within the document there are breaks between chapters, but no text reading “Chapter One,” Chapter Two… etc. I am exporting to .mobi & then previewing in kindle previewer.
Do not know what to do! It worked once and then…never again.
Also: is there a way to have all these various settings within Compile be the default so that I don’t have to keep doing them over & over, everytime I try to export?

I need clarification on a few points:

Does that mean you have the Text separator, illustrated with two text file documents stacked vertically with a line between them, set to “Section break”?

And if so, does that match the way you have the Binder set up… a stack of individual text files one after the other, one for each visible section of the book, with no exceptions?

I ask because separators are ignorant of depth. If you have groups of text files representing chapters, you’ll get multiple sections per intended section, when setting the Text separator to “Section break”.

Does that mean you have something like the following listing:

Title Page Dedication Forward 1 2 3 4 5 ...

Scrivener needs to get these titles from somewhere, do you use numerals anywhere in your project and have you examined all of the rows in the Formatting pane to check for bare numerals?

I don’t know what that means. Are you referring to your project, the Mobi file or what? What are “breaks” in this particular context?

Can you think of anything crucial you might have changed between then and now?

You can either create a starter project with all of your preferred custom settings (see §7.7.2, pg. 61 of the user manual PDF), or create custom compile presets (see §24.5, pg. 356).

Yes, the Formatting pane is in fact where the prefix/suffix code is set, so you’re already in the correct location to check for that. It sounds to me as though you’ve perhaps set up the “Chapter <$t>” code in the wrong Formatting rule type. Perhaps you’ve assigned it to folder type files, not text type files? Just click on the type of icon matching what you use for chapters, in the top section of the Formatting pane, and make sure the mock editor below looks right. You most likely do not want “Title” enabled as that will print the numeral, too. Supplying a prefix without the Title checkbox will rewrite the binder item name with a generic value as you supply it, and this will generate the ToC accordingly.