As you are able to import successfully from local drive, then there can be some issues with the read and write permission on your flash card.
So please make sure you have rights to make changes to your drive.
Please try giving permission to it by following the below steps:
1. Go to Finder > Select your card> Ctrl click on it > choose File > Get Info.
2. Click the lock icon to unlock it, then enter an administrator name and password.
3. Check whether you have read and write permissions or not. If you don't have it then change it to both read and write permission
4. Click the Action pop-up menu, then choose “Apply to enclosed items.”
Then try to import from your flash card in Lightroom.
Please let us know if it helps.
I've double checked and all files are readable, ie, I can copy them into another folder without entering admin password.
Would you please try to import the files from the copied folder now.