I often like to run the "verify disk" command on my cards from time to time to help ensure that they are in good working order and that there aren't any obvious problems with them. That tool is capable of repairing any type of hard drive and a memory card which is effectively just a small SSD. Within the applications folder of your computer is a folder labeled "Utilities," inside that folder is a tool called "Disk Utility" that you may have used in the past to help diagnose or fix issues with your Mac. A simple solution that will ensure this problem never presents itself is by manually copying the files to your hard drive before even bothering with Lightroom import. In my experience, for many users, it is far too easy to accidently import directly from the card, this can lead to accidently deleting your images or even having all the images go missing in Lightroom the moment that you eject the card. When importing images from a card using Lightroom you have the option of importing images directly or copying them to your computer first. Copy Images to Your Desktop Before Importing Them Leave them on the card until you are confident they are backed up then reformat. Or better yet, just don't delete files directly off the card. Always make sure to empty your computer's trash if you have deleted files on the memory card.
This can lead to a situation where a full card appears empty because all the files are in the trash bin that is only visible on your Mac. When a file on the memory card is placed in the trash it is actually stored in a hidden trash folder on the memory card, it isn't actually deleted until you empty the trash. Meanwhile my third party reader works great, never has problems, and is much faster as a bonus. I use them when I have to, but for everyday use I constantly have issues with them not discovering the inserted card or randomly ejecting the card.
Moreover, in my experience the card readers built into Mac computers tend to have issues. I think, in general, this goes without saying the cheapest USB card reader from the local Best Buy is cheap for a reason. In this post I will share a few strategies to help you avoid a headache when dealing with memory cards. Personally, I almost never have issues but I happen to also be the guy all my friends flock to each time they are having issues with photos on cards. Apparently issues with memory cards are quite common, even among Mac users.