EXIF lost when copying DNG to remote folder

Hello,

I work with Lightroom Classic 13.0.1 and MacOS Sonoma 14.0.

In my workflow I keep my recent DNG files on a SSD for easy and quick development. Once in a while my SSD gets full and at that moment I move most of the DNG files to a remote location (Synology NAS) by dragging the folder within Lightroom. Normally this works like a charm. Today I did just that, but I noticed the copied files lack EXIF information because some smart collections based om dates suddenly seemed empty.

What did I do wrong to loose the EXIF data? And is there a way to recollect the lost EXIF data?

Thanks for your help!