Thank you for your reply. In this case, rather than a URL link, I dragged or copy-pasted the images directly into the note. I have left the note open for an hour or more thinking it might be load time, but they have not appeared yet.
Unfortunately, I don't have the original URLs for the files. I just copy-pasted the images into the note, not thinking that would be a risk for losing them entirely.
I am not a paid subscriber and the website does not let me open a support ticket. Does Evernote not offer any support whatsoever for free-tier end users? The issue seems to be with the app, and the only way to recover the images being through the back end.