This is a recurring problem for me. If there are 200 files in a folder, at least 10% show a preview and viewer image that is not the same as the selected thumbnail. It is showing an image from some other file in the database. I have tried "force update" and update cache only. I have not tried reloading metadata. Nothing fixes this problem.
Neal
This sounds like you use versioning and proxy images?
This would explain that?
Tip: Check the Version panel for one of the problem files to see if there is a proxy image in use.
See also Visual Proxy (https://www.photools.com/help/imatch/#viewer.htm?dl=h-22) in the Viewer help (similar option also for the Quick View Panel, in the context menu).
No version or proxy problem. I find the only thing that works is to copy the image, open the copy in Photoshop, save as itself and then import it into the original location.
You did not tell us which file format you are using or what your workflow is.
IMatch is using an embedded preview / composite image or the thumbnail, if large enough.
Maybe these files have different previews/thumbnails than the 'real' image, for some reason?
Do you have a sample image which exhibits this problem so we can have a look?