All looks good on your SD card contents.
It is most likely to be a joint problem on the SD holder or the chip.
If you have a multimeter, use the continuity (beep) function (or low resistance range) to check the 4 connections between the SD card holder and the chip itself (not the pads).
Here’s the schematic:
Make sure the Makerbuino is switched off (or the battery removed) and make sure you have good continuity (low resistance) between one line of the SD card holder and the other end of the same line at the chip.
If you need more guidance on how to do this then do say so, I’m always happy to help.