Header issues with veryplaintxt 4.6.1

Can anyone help me figure out what is going on with my template? Warning: I am very low-techy-savvy!

When you go to the main page, you get the title and header image, but not the links to pages.
https://www.postandlintelblog.com/

If you click on a post title, the header image disappears and is replaced by a link in the form of the words “Header Image” — but the links to pages appear.
https://www.postandlintelblog.com/archives/27

If you then click on the page “About”, you get all three, just like they should be!
https://www.postandlintelblog.com/about

I’ve tried looking through the html in Edit Themes and I just can’t figure out why the three different pages are doing different things. I would like, obviously, to have the links to pages and the image to appear on all the pages. Does anyone have any insight?

Thanks much!!
Amy