Uninstalling old version breaks windows preview handler for new version.
When uninstalling an older version of illustrator, the windows preview handler for AI files gets removed such that it no longer functions for newer versions of illustrator that are already installed. The only resolution is to uninstall the newer version and reinstall which can be a pain, or manually modify the registry entries to assign the PDF handler to AI files.
Please get in touch with us at any of the other support channels – https://helpx.adobe.com/support.html . Since this is not a generic issue that we can reproduce at our end, we will need someone to look into your machine to figure out what is going on here.
Note, this issue is reproducible, it happens to multiple people in this office. When we upgrade to a major new version of AI, we usually keep the old version installed just in case the newer version has issues. When anyone eventually uninstalls the older version, the windows preview handler gets removed even though the newer version of AI is still installed.
Install the latest *two* versions of illustrator.
uninstall the older version and windows preview handler gets removed.