*Update - deleting the page and re-creating from scratch ( i.e. re-placing the existing blocks ) seems to fix this issue.
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Working on a custom page type which was working in (site/page_types/custom_page_type.php),
I then copied it to my themes directory for further "customization".

In attempting to add a custom header for this page type, it stopped loading the header and now page loads only the html content without the header.php file.

Removing the file from my theme directory has no affect,

I have no idea how to get the page type to load the header... any ideas?

thanks in advance