Those errors are not normal. The first two relate to the dc:identifier element which is a required element and is not supposed to be blank or absent.
As for the third item, that looks like a Kobo epub which has structural issues.
The following snippet is the first 7 lines of the .opf file from a blank ePub3 generated by Sigil. The identifier, language, title and modified items MUST be present for an ePub3 file.
Code:
<?xml version="1.0" encoding="utf-8"?>
<package version="3.0" unique-identifier="BookId" xmlns="http://www.idpf.org/2007/opf">
<metadata xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:opf="http://www.idpf.org/2007/opf">
<dc:identifier id="BookId">urn:uuid:982c9231-abdd-4c4c-9ff5-d4814ae29041</dc:identifier>
<dc:language>en</dc:language>
<dc:title>[Main title here]</dc:title>
<meta property="dcterms:modified">2025-03-23T18:40:12Z</meta>