STM32 and SDFat - Can't create file in directory in SD
I found the issue. I'm not creating the directory folder properly. When I checked the SD card from another device, the DATA folder was invalid, and creating it manually works. I'll look for a solution and post an update.

UPDATE: https://forum.arduino.cc/index.php?topic=421131.0 I'll try this tomorrow but it'll probably fix the issue.