Some SD Cards Not Working Properly With 2021 14 and 16-Inch MacBook Pros

The SD card reader slot on the new 14 and 16-inch MacBook Pro models is not functioning as expected with some SD cards, according to multiple reports on the MacRumors forums.
In a long complaint thread, MacRumors readers have detailed the issues that they're having with some SD cards, and there seems to be little consistency between reports and affected SD cards. Some SD cards crash and can't be accessed, while some have unusually slow transfer speeds. MacRumors reader Wildct explains the issue: