"Missing Attachment" In Image Gallery

I am having an issue where the native WordPress gallery functionality is not working on my site. I can insert individual photos but once I try to make them into a gallery I get the error “Missing Attachments”. I have tried re-uploading the images but that doesn’t seem to fix the problem.

Any idea of what might be causing this or ways to test/solve the issue?

Any help or guidance would be very much appreciated!