Have the same problem with my Raspberry Pi 2 with IQaudio PI-DAC+.
Initially thought the micro sd had died, but I have no issues accessing and writing to it when I plug it into my computer.
Edit: I have managed to sucessfully rollback my installation to 2.587!
On the micro-sd card there are 3 partitions. There is the fat32 partition for booting, the volumio partiition (with tarred kernels and sqsh file system) and volumio_data (containing any filesystem changes, like configs and additional software).
To rollback my installation, I deleted “kernel_current.tar” and “volumio_current.sqsh” files and copied and renamed the “kernel_fallback.tar” and “volumio_current.sqsh” files to current. I then extracted the contents of “kernel_current.tar” into the fat32 boot partition but kept the config.txt and cmdline.txt files that I already had (as they were customised).
When I put the microSD back into the Pi and turned it on, it booted back up into Volumio with no issues.