Table of Contents Not Sequencing/In Order

I have Paragraph Styles:
Header 1
Subheader 2

Subheader 3

Subheader 4

There are some sections that do not have a Subheader 2 (more than 2-tier hierarchy).

I generated a table of contents, but they are not listing in the correct order, as in Header 1 is showing up below Subheader(s). Headers are in a different text frame on each page, but didn't think that mattered, as the rest of the document is essentially in the right order; it's just the Headers showing up at the end of the sequence in the TOC rather than at the beginning. E.g.:

Header 1A

Header 1B

   Subheader 1C
   Subheader 1C

   Subheader 1C

Header 1C

Header 1D
   Subheader 1D
   Subheader 1D

   Subheader 1D

Header 1E

   Subheader 2E

   Subheader 2E

   Subheader 2F

   Subheader 2F

Header 1F

etc...

I have rearranged the TOC levels, even removed and recreated the TOC with no luck.
Any ideas?