Further diving is showing that there’s issues with the FatFSInterface and the bootloader:
This object has some memory limitations due to the media connected to it. The SDMMC1 peripheral can only communicate with the AXI SRAM, and the DTCMRAM cannot communicate with the DMA. So the FatFSInterface object should always be located in the AXI SRAM. This is the default location for all data/bss memory using the standard build. However, applciations using the electrosmith bootloader will need special consideration when using this object AND an SD Card.
So at least there’s a string to tug on.