if there is a space after comma images are not added to the document
src="data:image/jpg;base64, iVBORw0KGgoA
this is perfectly acceptable and most often the developer doesn't have control over on removing the space in the data URL, and is perfectly valid to have space there. you have to trim the space I guess to make it more reliable.
It took me more than a day why html renders properly, pdf convertors working properly but not html2docx. See attached sample to test.
Thanks
mydoc.html.txt