Steps to reproduce:

Create word docx

1. Add multiple pics to it, 3 works. (or use attached document)
2. Attach document to a confluence page
3. Use viewdoc macro to render document to page.
4. Save page and view that not all images appear.
5. Refresh page to find a different set/subset of images render while another image does not render.

Env. conf 5.1.4/java 7/mysql

Workaround:

Downgrade Office Connector plugin to v2.1.10 instead. This plugin version is compatible with Confluence 4.1.2 - 5.1.4 as per this page.

You may remove Office Connector plugin from ConfluenceInstall\confluence\WEB-INF\atlassian-bundled-plugins and replace it with Office Connector v2.1.10 and restart Confluence afterwards.