IMAGE TEST B - large data URI (real screenshot)
Edited
A real help centre screenshot, 86,145 bytes, embedded as a base64 data URI (114,882 characters in the CSV cell).
What to look for: the Vehiso customers list. If A renders and B does not, there is a size ceiling rather than a blanket rule against data URIs.
After importing, also open /en/articles/<this article id>.json on the published knowledge base and read the html_content field. If the image survived, the interesting part is what the src became: a frontkb-cdn.com URL means Front decoded and rehosted it, an unchanged value means it was stored verbatim, and a missing <img> means it was stripped on import.