The first thing I noticed is your image link
(below in the link section ignore the " because without the " the \ is removed for formatting reasons i guess. After posting it just looked like a bunch dots .........\documents instead SO I went back and added " after )

Ive had this issue. Im not sure why but sometimes zettlr adds more of the directory things "..\" after changing folder/file structures or something like that. the "..\" takes the place of "C:\YOURDRIVE\user\ACCOUNTNAME\Documents\ etc.." I think one of these "..\" equals one folder/directory. for example ..\ equals C:\YOURDRIVE.
If it were me I would delete some of those ..\
it would look like this:

If that doesn't work try deleting that and drag and drop your image back in there.
As far as exporting goes how many formats have you tried when you export your Document? Compare them. For me I only have exported my documents in PDF or HTML. I get images most of the time, but some arent in there and there are formatting errors. I think formatting gets messed up in the conversion process. Zettlr is a work in progress.
When I export into HTML I can manually edit the html to fix the formatting and images that don't appear. From there you can convert the html to pdf with software of your choosing.