This issue is happening with Acrobat Pro and Illustrator. I am on Windows 10 Pro. It happens with any dialog box from those apps - so I could be trying to place a file, or open or save. There are no PNG thumbnails. The PNG thumbnails show in Windows Explorer and Adobe Bridge just fine.See screenshot - I overlaid an open dialog form Acrobat with an Explorer window to show you the issue with the thumbnails.
Changing the file association to different picture viewers, including Photoshop, has not changed the behavior. That issue is not affecting JPGs and TIFs.
Any tips on how I can fix that so I can see PNG thumbnails when opening/saving/placing files in Illustrator and Acrobat?