Site shows themeless and blockless front page
I would check your watchdog logs (/admin/reports/dblog) after refreshing your homepage a few times.

This may give you some clues to what the problem is. For example...

I ran in to a similar issue with my D7 -> D8 migration, where my nodes were imported with a 'filtered_html' input_format. I was storing my node body content as markdown.

My front page had no blocks or theme. When I looked in my logs, I was seeing Missing text format: filtered_html.

I ran the following to update the input_format of my nodes, which fixed my problem.

UPDATE `node__body` SET `body_format`='full_html' WHERE `body_format`='filtered_html';


To then get things displaying properly, I installed the markdown module (and one of the required libraries, I opted for commonmark).

drush en markdown
composer require league/commonmark


I then went to /admin/config/content/formats/manage/full_html and enabled markdown for that content type.