Also, to be explicit: save data is not at risk at all. Saves are stored on the internal NAND, which uses FAT32/doesn't corrupt. The only data at risk are downloaded games/other SD card files, and those can be redownloaded. The absolute worst case is you lose some screenshots.
According to him, it seems to be related to the Switch's current exFAT driver, which means you may have issues if your SD card is formatted to exFAT (default on cards larger than 32 GB).
What that means for the average user:
(A) Don't panic. Your saves aren't at risk. Worst case is you have to re-download the games, but your data will still be intact.
(B) If you're really concerned, you can re-format your SD card to be FAT32 and avoid the issue. Needless to say only reformat if you know what you're doing.
(C) Still no concrete evidence for the cause. Autosave may be a placebo.