Thank you.
That is the problem then. The custom field on image options only works with post meta, but not user metadata. I think however it might be possible to resolve without access, using a custom code.
I have made a custom snippet to try. Add this custom code to the functions.php in your theme/child theme directory (copy from line 3 only!). Before editing, please make sure to have a full site back-up just in case!
This will parse the user meta from the image field, and change the image to it if available.