Setting the ComplianceLevel to PdfA3B and the TaggingStrategy to UseExisting when exporting a PDF document leads to the following Error reported by VerPdf:

Specification: ISO 19005-3:2012, Clause: 6.2.11.5, Test number: 1
For every font embedded in a conforming file and used for rendering, the glyph width information in the font dictionary and in the embedded font program shall be consistent.
Glyph width 274.4140625 in the embedded font program is not consistent with the Widths entry of the font dictionary (value 272)