Star ratings do not 'stick'.

[rafiki]

When I apply a star rating to an image it shows up in the taskbar at the bottom of the screen but as soon as the metadata updates, the star rating disappears. Colour labels work fine. These are Canon CR2 files from a 5D Mark IV. What could be causing this?

[Mario]

See https://www.photools.com/community/index.php?topic=4102.msg27503#msg27503

[rafiki]

Thank you. I see the fix in the link. I am not familiar with the EXIF tool; is this a one-time exercise which runs automatically from then on, no further action needed or must it be applied again with new images as they are imported?

[Mario]

This needs to be done once per file (you can fix the problem for any number of files that way).
Try to prevent your camera from adding a "No Rating" XMP record to your images. Ask Canon support how to do that if you don't know how.

An alternative would by to change the settings for CR2 under Edit > Preferences > Metadata 2: File Formats. If you switch the "XMP Sidecar file" to "Favor XMP sdecar file" IMatch ignores all embedded XMP metadata in the CR2.
it depends on your workflow and the data your camera writes if this is OK for you. Ask Canon support for more info.