Images missing when publishing online

What version of InDesign?
What OS is it and version number?

Can you publish a simple document online with images - or is it just this one document in particular?

How are the images linked - did you use File>Place - did you copy and paste them in - are there image links in the links panel?

Can you share a sample document or the link to the published online?

Here's some standard things to try

If a document is not behaving well then try 

File>Export 

Choose IDML

Open the IDML in InDesign
Save the file as a new InDesign file with a new name
See if the issue persists.

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Try resetting your preferences:

Windows: Start InDesign, and then press Shift+Ctrl+Alt. Click Yes when asked if you want to delete preference files.
macOS: While pressing Shift+Option+Command+Control, start InDesign. Click Yes when asked if you want to delete preference files.
A dialog will appear asking to delete the InDesign Preferences, select 'Yes' on this dialog.
Further info and instructions here if needed:
https://helpx.adobe.com/in/indesign/kb/indesign-preferences-support-file-locations.html