It does not increment because your heading structure is a real mess!
After a Heading 6 paragraph like “Apendice A”, you insert a Heading 2 one like “Plavras …” which brings you back to level 2. Next time you type a Heading 6, it starts a new level 6 after the latest higher-level heading, in this case Heading 3 “Palavras emocionais …” on the page with the gradient table.
Your confuguration will not work if you revert to levels 1-5 after a level 6.
Having alphabetical appendixes after numbered chapters is a bit tricky but not difficult. Search this site for complete solutions. I’ve already provided several, amongst these one is very extensive.
Basically, you have two solutions:
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split the Heading n family into two parts: 1-5 for numbered chapters, 6-10 for appendixes
This means once you have begun styling with 6-10, never reuse 1-5 or you’ll experience your present mishap. This implies that formatting is made the same for 1+6, 2+7, 3+8, … Heading 6 is similar to Heading 1 for appendixes, as are Heading 7 and Heading 2, etc.
This is a quick and dirty hack. But it has many inconveniences because it twists the real structure of the document
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create new paragraph styles known to the TOC machinery
This requires to create a new list style (the appendix counter) to attach to new paragraph styles for the level 1+ of the appendix. This is more professional and more reliable but I’m afrais it is beyond your present reach. It is extensively explained in one of my answers but I have no time in the instant to search for it.
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