I can think of two possibilities
- The speed of writing data to the card and then reading the data from that same card to add to catalog is slow enough that Lightroom has to pause and wait for the data to be written or read to the card
- There is some hardware malfunction of the card reader or card
Thanks but I'm still stuck. Moving the catalogue to the same card where the images are didn't improve the 'not responding' problem. Export without adding to catalogue is still OK.
I can't imagine how moving a catalog to a card would help. That seems like it would just make things slower.
My point with #1 is that maybe it can't be done without such a delay. My point with #2 ... well, it doesn't sound like you checked a different card and a different card reader to see if your hardware is malfunctioning.
Why do you need to add the photo to the catalog? A lot of people don't bother keeping or adding the export to the catalog. Something to think about.