Recent changes to the TEI P5 standard have made the idno (id number) element invalid as a direct child of the biblStruct element. The Zotero (4.0.29.10) export to TEI produces structures like this:

<biblStruct type="journalArticle" xml:id="Abrahamse1994"
corresp="http://zotero.org/groups/263360/items/SKJHCUNV">
<analytic>
<title level="a">Surname analysis for estimating local concentration of Hispanics and
Asians</title>
<author>
<forename>Allan F.</forename>
<surname>Abrahamse</surname>
</author>
<author>
<forename>Peter A.</forename>
<surname>Morrison</surname>
</author>
<author>
<forename>Nancy Minter</forename>
<surname>Bolton</surname>
</author>
</analytic>
<monogr>
<title level="j">Population Research and Policy Review</title>
<imprint>
<biblScope unit="volume">13</biblScope>
<biblScope unit="issue">4</biblScope>
<biblScope unit="page">383-398</biblScope>
<date>1994</date>
<note type="accessed">2017-01-18T23:22:45Z</note>
<note type="url">http://link.springer.com/10.1007/BF01084115</note>;
</imprint>
</monogr>
<idno type="ISSN">0167-5923, 1573-7829</idno>
<idno type="DOI">10.1007/BF01084115</idno>
</biblStruct>

where the idno elements actually belong inside the monogr and analytic elements respectively (the ISSN refers to the journal, presumably, while the DOI refers to the article). If anyone can point me at the code repo I may be able to contribute a patch, although discovering the correct location for a given identifier is not trivial.