I have several SD cards used to store photos on game cameras. They work reliably on my PC but inconsistently on my iMac. When I insert one of them into the back of my iMac to read the photos, it works only about 25% of the time. Most of the time, the SD card doesn’t even appear on the Mac. While on my Windows computer, all the SD cards work 100% of the time. What gives, Apple? Has anyone had the same issue and how did you resolve it? I just want my iMac to read the SD cards as reliably as a PC. How hard can it be?
I’m prone to believe that the issue is on the SD slot of your iMac.
The SD cards all work on PC, so they are not broken. Yet they all have issues with your iMac, suggesting that the problem is on your iMac. If there’s an Apple Store nearby, take your Mac for a service. Have them check the SD card slot to see if it’s loose or has other issues.
Another thing to consider is whether your SD card is turned on all the time. Chances are that you forgot to unlock the SD card at times.
I find this article useful: How to Fix SD Card Not Mounting on Mac?