In the default theme, with no changes at all, I'm getting error messages that the following media files are missing.
/wp-content/themes/pure-line/library/media/images/change-close.png
/wp-content/themes/pure-line/library/media/images/search-text-back.png
/wp-content/themes/pure-line/library/media/images/search-text-corners.png
/wp-content/themes/pure-line/library/media/images/field-text-left-right.png
/wp-content/themes/pure-line/library/media/images/logout.png
I've already fixed these myself by removing the calls to these files. But I'm not sure why those files would be missing in the first place.