Any way to update_post_meta with html content? It gets stripped and becomes empty

I believe the problem is with your use of sanitize_text_field (line 668 in your pastebin), which will strip markup. Proof of concept:

$str="<p>Howdy Ho!</p>";
echo $str;
echo sanitize_text_field($str);

You will need to use some other function to clean the data… possibly wp_kses

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