[KevinH]

Editing the TOC, unless you hit Cancel will create a new standard Sigil format TOC.

It sounds like you hit OK which causes the rebuild. It does not matter if you changed anything or not, Sigil takes the information given by the Edit TOC and recreates the TOC from it. That is expected behaviour.

It also sounds as if you are now missing a link to a css stylesheet for that nav that controls the numbering or not. A standard Sigil format Nav typically includes its own linked stylesheet. Simply editing that newly created stylesheet will enable you to control the numbering and what gets hidden.

FYI, people often add and remove headings and chapters while editing, and so it is often easier to simply generate the entire TOC using Sigil tools once near the end, editing it as needed in the TOC editor, or editing the Nav directly in CodeView before going final. Editing a custom TOC not originally generated by Sigil may not be what you want, especially if you did not Cancel or exit that Dialog.

If you do not like that change, assuming you have created a Checkpoint (which is always a good idea) you can easily revert.