Word is the glitchiest program I've ever encountered, and your experience sounds painfully familiar. I don't know whether you're running into a file-size limit, or the program doesn't like that particular photo, or the moon is in Jupiter with Scorpio rising... but Word doesn't need
a reason to be contrary, anyway.
It's possible that the photo is corrupt in some way, though. Maybe you could try recreating the jpg (or whatever you're using) from the original photo file and see if Word likes it any better.
Failing that, you could separate the document into two segments, rather than one big file... in case it really is
a size limit issue. (Save a duplicate, then delete a different half of the material from each one.)
Sometimes it can help to resave the entire document, too -- using "Save As" and retitling it. Don't know why, but sometimes it helps.
Also... I come from the old days, when if you ran into trouble, you just rebooted the machine. Sometimes it still works!