I tested 10 cards on my PC. I ran a check for errors on each card, only one of the ten had any errors. 8 of the ten are cards that had played just fine on my Pono till the beginning of the year. The other two are brand new cards which had not been used yet. I reformatted both of those on the PC. Neither had errors and worked fine on the PC, but neither would load on the Pono. Even without any files on them.
Same with the other 8 cards, none would load on the Pono. I did play audio files on all the cards just fine on the PC. However, I did notice one thing odd. Any files I added to those cards after 2017, most likely using the PMV, those files did not play, some even had duplicate files that would not play. So I deleted those, but the cards still did not play on the PONO. So either the PMV or my iMac did corrupt some files since the start of 2017. However, the SD cards that had no files on them or had no bad files also did not load onto the player.