PDF export shrinks the embedded photo inside a SVG-image

I got a pdf image from a customer. I converted it to svg with inkscape to insert it in an OnlyOffice document. A photo (pixel image) is embedded in the svg image.
Everything looks good in OnlyOffice but in the exported pdf document the photo is shrinked horizontally (see screen dump). The vector parts of the image are displayed correctly.
This is particularly annoying because it only became apparent in the finished print product (my fault). What is happening here? Is there an error in the PDF export routine? Can this error be prevented (apart from only importing pixel images into OnlyOffice)?
I uploaded the docx and pdf files.

OS version: Linux Mint 20.3 Cinnamon
App version: ONLYOFFICE Desktop Editors, Community version 9.3.1.8 (x64 flatpak)

Back.docx (5.9 MB)
Back.pdf (352.9 KB)

Hello, @ToxyLT

Thank you for the information and for the files you provided. We are checking this behavior on our side now and will get back to you as soon as we have more information about the cause of it.