I was just experiencing this today, with a new card as well. I could not fix it from within Batocera. What I did was flash Raspberry Pi OS to another SD card, booted from it and connected my Batocera SD card with a USB reader. Then I ran fsck on the partitions on my SD card with the -y option. It found some issues and cleaned them. When I booted from the Batocera SD card again I had no more ‘bad block checksum’ messages.