OK, obvious ones, is the card at least trying to conform to the standard (MBR, FAT16/32/64, and with the matching partition type)?
(official Swiss is actually built with GPT support, but let's keep thing simple and widely supported here)
Which version of Swiss? (it can self-update but obviously needs to be SD2SP2 compatible in the first place to reload itself from there, if you have version 630 or whatever it's definitely new enough, FWIW I bought an SD2SP2 + updated Swiss miniDVD combo back in 2019 to upgrade the disc + XenoGC + SD Gecko combo I bought in 2018
)
Nothing else is on the EXI bus number 2, so by this point the only plausible issues are bad connections, a card that doesn't like SPI mode (so, not a good faith SD/MMC), or a card that has problems with 32 MHz speed (are those a thing? 16 MHz only operation is usually caused by filtered card adapters like the official DOL-019 or the Datel)